Depends. Even given the same variety of tea, caffeine levels can vary based on the season, where and how the tea was grown, particular tea bush/tree, how the tea was brewed, and so on. For instance, younger tea plants contain more caffeine (apparently).
Furthermore, caffeine is not the only stimulant in most natural products which contain it:
Wikipedia wrote:The disparity in experience and effects between the various natural caffeine sources could be because plant sources of caffeine also contain widely varying mixtures of other xanthine alkaloids, including the cardiac stimulants theophylline and theobromine, and other substances such as polyphenols that can form insoluble complexes with caffeine.
Different people have different reactions to these different chemicals, which means that a beverage which is stimulating for some may not be for others. Further complicating the matter is the fact that tea also contains theanine in varying quantities, which generally produces a relaxing reaction, but again, different people will experience its effects to varying degrees.
Also keep in mind that a single person's sensitivity to caffeine is not constant as well; it changes over the short term based on factors like your stomach content, or the presence of nicotine or alcohol in your bloodstream, and over the long term based on factors like your level of caffeine tolerance.
So, to answer your question... there is no real "truth"; there are simply too many variables to make such a thing easy, practical, or worthwhile to measure. In my personal experience I have generally found that Japanese sencha gives me the greatest kick, while black teas are generally most relaxing... but that is just me, and only sometimes.