The Mighty-Multi-Mite Challenge
Introduction
Yeast extract is a by-product of the beer brewing industry and is used in various foodstuffs. The most famous of these are Vegemite (orig. Australia, 1923) and Marmite (orig. United Kingdom, 1902). In both countries these respective foodstuffs are part of the national identity, with admirers of each who would not eat the alternative from the other side of the world if given the choice.
It should be noted at this point that the author is British and as such is a lover/addict of Marmite. Until this matter arose he cared more about such subjects as the air-speed velocity of unladen swallows than the existence of Vegemite, which is to say: not a lot. Despite this, and a mild aversion to all things Australian (apart from Rolf), he will strive to remain impartial.
The idea for the test that follows came about when the author was discussing the two products with his girlfriend who revealed that during her time spent in Australia she had come to prefer Vegemite to Marmite. The author was shocked and horrified that a Briton could hold such an opinion and came close to ending the relationship then and there. He did not, but this distracts from the experiment.
For several days, and with the absence of his girlfriend, the author contemplated her comments and came to the conclusion that there could be some truth in the opinions of this lady, due to her possessing considerable intelligence. A discussion with a colleague, whom the author considers a clever chap, revealed that he too preferred Vegemite to Marmite. It appeared to him that the only way to disclose the truth would be a head-to-head taste test between the 'Mites':

The Mighty-Multi-Mite Challenge!
Literature Review
In common with all research previously done by the author on any subject libraries were shunned in favour of the more time-efficient (read: lazier) Google option. Four critical facts came up during this review:
1. Ingredients difference: Vegemite contains caramel as a colourant but this may also affect the flavour through a sweetening effect.
2. 'Marmite-resistance': As noted on The Marmite FAQ Marmite has "drug-like qualities" by which they mean that "the more you eat, the thicker you need to spread it to get the same mouth-burning effect." This brought to the author's attention his own habit of spreading Marmite several millimetres deep on toast and sandwiches. The mouth-burning effect is remembered but has not been experienced for many years. This fact will be held in mind due to its possible affecting of amounts used and taste-testing.
3. The general consensus seems to be that Marmite has a stronger flavour than Vegemite.
4. People in Australia and New Zealand may be used to Marmite as manufactured by The Sanitarium Health Food Company which contains an abundance of sugar so writings from these countries describe 'Marmite' as having a less-intense flavour than Vegemite. Despite never having tried it, the author believes that this Manky Marmite™ is so different in composition from British Marmite that it is an abomination for it to share the same name. It can be noted at this point that the Sanitarium Health Food Company is also responsible for supplying unlucky Australians with Weet-Bix, a poor emulation of the delights of genuine Weetabix.
Remember kids:

Despite these not-quite-right products it should be announced with positivity that The Sanitarium Company promote healthy eating and vegetarianism.
Predictions
Marmite will, in every way, be superior to Vegemite in all tests.
Method
Marmite is used in three main ways by the author who will use Vegemite in the same three ways to directly compare the two Mites.
1. Mite on toast: the original way to enjoy Mite. Both Mites will be spread on buttered toast and their tastes compared.
2. Cheese & Mite sandwiches: portable yeasty pleasure. Vegemite in place of Marmite in simple sandwiches made using cheese, butter and the cheapest-of-cheap white bread.
3. Hot Mite Infusion: controversial B12-boost. Many people have discovered the joy of pouring hot water into an 'empty jar' (i.e. not containing enough for knife-based extraction) of Marmite and drinking the brown stock that ensues. Many people consider this practice abhorrent. Despite their criminal history and Fosters-addled minds, the kangaroo-chasing pseudo-cricketers must have discovered a similar brew using their wrong-Mite. Oh yeah, "impartial", right...
Implementation
1. Mite on toast
Two slices of bread were toasted to perfection before having butter spread thickly and evenly over one surface of each. To this surface either Marmite or Vegemite was applied respectively, using two separate knives to avoid cross-contamination. This was repeated at least three times with the only change in method needed being the amount of Vegemite used in comparison to the amount of Marmite used due to preliminary findings of intensity of flavour. More repetitions were done over the course of the next few days.
Fair testing: In all cases water was taken between bites of each to remove residue flavour. The order in which the two Mites were tasted was varied.
Fig 1. Mite on toast

2. Cheese & Mite sandwiches
Two slices of buttered bread had sliced mild cheddar cheese and Vegemite applied to each respectively before being brought together in the conventional closed-sandwich method. The amount of Vegemite planned was augmented prior to implementation as a direct result of the Mite on toast test. The sandwich was cut in half lengthways (NEVER diagonally...), wrapped in clingfilm and taken on a train journey as sustenance. Accuracy in comparison was assured by forgetting about the sandwich until the return journey thus ensuring it was as squashed as all sandwiches carried on train journeys in back packs.
Fair testing: No Marmite sandwiches are necessary for comparison as the taste of them is as well-known to the author as the taste of bamboo is to pandas, eucalyptus to koalas and Australian surfers to Great White sharks.
Fig 2. Cheese & Mite Sandwiches

3. Hot Mite Infusion
Half a teaspoon of Mite was dissolved in (recently) boiling water and the resulting drink consumed. Again, it was thought necessary to adjust the amount of Vegemite used in light of previous tests: approximately three-quarters of a teaspoon was used. A further test was carried out on a later date using the more correct method of pouring boiling water into the almost-vacant jar of Vegemite, stirring and drinking the result.
Fair testing: A clean palate was ensured between samples using Lipton Ice Tea, the author being too idle to open a bottle of water.
Figs 3 & 4. Making hot Vegemite infusion

Results
General differences
Before experimentation began differences were noted between the two Mites. The first was the appearance. Marmite has a very glossy sheen whereas Vegemite is a slightly more matte shade of brown. This is an aside and has no affect on the results. The smell, however is one of the major differences between Marmite and Vegemite: it is noticed immediately upon opening the jars. Like all smells associated with unique substances the difference defies description other than through a subjective comment: Marmite smells like Marmite while Vegemite smells similar to Marmite, but somehow more intensely so. Despite the scientific nature of this paper, reviewers will excuse the author's use of the word "weird" to describe this phenomenon.
1. Mite on toast
The test was carried out as described. Another difference was noted as the Mites were spread: Vegemite is far less 'runny' than Marmite and remained so even on contact with warm toast. This resulted in an inability to mix Vegemite with butter and form a butter-Mite 'paste' that the author enjoys when spreading Marmite on toast. When it came to actually consuming the toast it was the difference in smell that was again first noted. The volatile odour of the Vegemite was intensified by being on warm toast, but the taste was not. Marmite smelt mellowly of Marmite and filled the mouth with an incredible flavour of yeast-based goodness.
Due to Vegemite's seeming 'lack' of flavour the test was repeated with more Vegemite. This brought the flavour more into line with Marmite but also increased the peculiar odour.
2. Cheese & mite sandwiches
When the sandwiches were finally consumed they tasted exactly like Marmite sandwiches. The cheese was even pleasingly stained brown by the mixing of Mite and the residue (or 'sweat') exuded by the cheese, just as with Marmite. The weird Vegemite smell had diminished, possibly due to the time scale and also by having the Vegemite contained in a bread-based setting.
3. Hot Mite Infusion
Appearances were observed first and it was noted that the Vegemite-based beverage was much more opaque than the tea-coloured Marmite drink. Upon consumption the major difference was again firstly the smell. The Vegemite smelt of warm beer, not unpleasant, though again a bit odd. Tastes were again, indistinguishable. The increase in amount was unnecessary as the second, jar-based method showed.
Conclusions
Taste has been found to be almost irrelevant during the course of this test. Both Mites are good and tasty. The slightly stronger taste of Marmite means that less has to be used to achieve the required effect but the actual tastes of the two Mites are very similar; almost interchangeable. The author has just finished a mug of hot Vegemite drink and the aftertaste is identical to that of a hot Marmite drink. The difference in texture noted when applying Vegemite to toast meant a detraction from the Mite on toast experience.
So the conclusions must be drawn from personal preference. Those brought up with the stronger smell and weaker taste of Vegemite will not be accustomed to the weaker aroma of Marmite followed by a more intense flavour experience. Those used to the delicate bouquet of Marmite and looking for a mouth-melting hit will find the smell of Vegemite familiar but rather strong and indescribably odd. This smell is then followed by a disappointing lack of taste unless much more Vegemite has been applied for a given area of bread.
The main discovery coming from this investigation was quite unexpected and has disproved the prediction: Marmite was not superior in every way to Vegemite. Marmite and Vegemite are similar in many ways but share one vital difference: the smell. Marmite's tang leaves you with no uncertainty as to what is coming whereas Vegemite's stronger smell leaves a little to be desired on the palate upon tasting. There was simply not sufficient taste in Vegemite to do justice to such an emanation. Smell and taste are so strongly linked that a balance of the two is vital. This is an area that Vegemite loses in.
The author draws from this the conclusion that Marmite is the superior Mite. He could eat and possibly live with Vegemite, but his mind would be on Marmite and in a straight choice between the two it would be Marmite every time. It is noted that two intelligent people do not share this opinion, which merely leaves the author to question their expertise. One of them even has a MSc, compared to the author's BSc, which just goes to show that certificates don't earn you taste.
Further Studies
There are myriad ways that Mites can be used in cooking, especially as stocks, so an investigation into Vegemite & Marmite as ingredients may be worthwhile.
Despite the possible backlash from fans of both Mites there is the exciting universe of mixing the Mites in varying proportions to bring out the best qualities of each: can a Mite be achieved that combines the strong smell of Vegemite with the superior odour and stronger flavour of Marmite?
Due to a lack of further Vegemite in the author's laborappartment, and no great desire to purchase more, these tests will not be carried out in the near future.
Heck, what would be the point anyway? Marmite rules!