AAAAAAAAAAAAAH!!!! No on the Decaf. It's bad. Very, very bad. It's mostly made by soaking the leaves (or beans for coffee) in petrochemicals, and then quickly draining and drying them. This leaves residual petrochemicals on your tea. You're better off with the real thing.
Anywho, a little caffeine won't hurt you anyway, and may even prevent colon cancer. A great deal of caffeine is probably a bad idea, though. As for real tea, green tea generally has lower caffeine content than black tea, though not always. You'll need to experiment. You can get several cups of tea with only the caffeine of one cup by doing multiple infusions. You can usually get three to four cups out of one amount of most china green and oolong teas. Black teas, not so much.
As for other herbal "teas" (and red "tea" (rooibus)), they rarely have caffeine. Yerba mate and kola nut are the only exceptions I'm aware of. The quotes are there because they aren't really called tea. They're herbal infusions. People started calling them tea, because they can prepared in much the same way. Mint, chamomile and lavender are good herbal infusions to try. Watch out for artificial flavors in the blended packages.
Actual tea comes from the leaves of a specific plant (Camilla sinensis), and is available in a variety of forms. Black, green, oolong, pu-erh, and white are the basic types, with each having a serious variety of flavors based on preparation style and growing region. In general, oolong and white will have the highest quality since they are the most difficult to harvest and cure. My personal tea collection has over 70 different teas, and I can tell the difference between each one.
On red tea. In China, black tea is called red tea. You will rarely see black tea called red tea outside of China. You will, however, see an African root called rooibus sold as red tea. Is it caffeine free and has a spicy taste (not hot spicy but pumpkin pie spicy) which reminds me Christmas. I recommend it for the caffeine-averse.
On yerba mate. Mate doesn't technically contain caffeine. It contains mateine, a compound so similar to caffeine that it took many years of study before scientists realized there was a difference. Mate, to me, seems like it has less of a buzzy effect than coffee but more of a buzzy effect than tea. This is probably because tea not only has caffeine but a sedative as well, which takes the jitters out of the caffeine experience.  |