I am trying to find the best pick-me-up Japanese green tea and was wondering which type was the best to get from the assortment of Sencha, Gyokuro, Kabusecha, Bancha, etc.
From what I've read, caffeine content can be variable even within varieties. There are possibly seasonal variations, variations in harvesting and processing technique, variations in the original plants... Psychological effects (e.g. what smells perky to you) might be just as strong, and steeping for 10 minutes instead of 5 might make as much difference as any choice of variant. So take any answer with a grain of salt, and don't be afraid to simply go with what seems to subjectively work best for you.
That said, gyokuro is supposed to be stronger than other sencha teas, and I believe compared to other Japanese green teas as well. (I found similar information elsewhere; it's not just wikipedia.)
I agree with Jefromi, except that the powdered forms of Japanese tea (Matcha) may have significantly more caffeine in the final brew than other teas.
This is according to the analysis of 35 teas reported in the 2011 book Tea: history, terroirs, varieties. The table on page 254 reports matcha made with 1.5g of powder as having more than twice the caffeine concentration of any other tea brewed with 5g of leaves. The reported figures were averaged across three observations, but the analysis was hardly exhaustive, and there was a lot of variation even between two batches of the same type of tea, made the same way.
Matcha (powdered green tea) has the most caffeine from what I understand. Growing up, we were warned by grannies and aunts about it, and it was always taken in small amounts with Japanese sweets. According to one Japanese blogger, it has 50mg of caffeine per 150ml of matcha (half the amount in coffee which has 100mg of caffeine per 150ml). However, the effect of caffeine is dependent on how much is in the body, and she points out that tea tends to be much more drinkable than coffee in larger amounts so it all depends how much you drink in a day. On a side note, I vaguely remember a televised study saying that caffeine levels can actually peak and have the reverse effects (ie. cause sleepiness), so more may not necessarily be better lol...