I am a tea lover and a self-appointed tea snob.
I got addicted after I decided to kick coffee and go to tea instead. So, when I lived in Madrid I went to a tea store called Bomec (apparently where Victoria Beckham was buying her tea when they were still on this side of the pond! hahaha)... Not only did the employees know an amazing amount about the product, but they made me curious. Just how different is the quality of loose tea, and what are the differences in the various red teas, green teas, etc. Here's what I know:
FIRST AND FOREMOST: That stuff in teabags is crap! You get no benefit from it because it's basically the powder/shake that is left after the processing of higher-quality loose teas. The essential oils are gone, because the exposure to air dries it out completely before you even buy it! Therefore, you get NO BENEFIT AT ALL from tea in teabags, except for "flavor", which is infinitely better in loose teas anyway. If the idea of loose tea scares you, buy a metallic tea filter or empty bags, which you can fill up as you use them. You can get them online or at Whole Foods/Wild Oats/Trader Joe's, etc.
GREEN: There's Japanese, Chinese and even a variety from Ceylon. They all come from the same plant but they are processed differently. But the higher the quality, the better. I used to buy a Japanese green tea called Tokio T, which consisted of WHOLE leaves and orange rind. Now I stick to the (much cheaper) Chinese Gunpowder, which you can find at any Asian Market. Green tea has antioxidant properties, and drinking 5 cups of green tea a day has been shown to burn an extra 65-70 calories a day! It has also been shown to be somewhat of a cancer "blocker", with much lower rates of cancer among smokers in Asian countries with a high consumption rate of green tea.
RED: Rooibois is good for those who want less caffeine, and Pu-Erh is good for those who want to de-bloat. After any sodium-heavy meal I always drink a cup or two of Pu-Erh to get rid of the side-effects of all the salt. Again, buy it LOOSE! Also, Pu-Erh is aged like wine, and some people consider themselves "collectors" and "afficionados" of the stuff, so if you jump on the internet and see REALLY expensive Pu-Erh don't get discouraged - the cheaper stuff is out there. The stuff I used to buy in Madrid was reasonably priced and had a great taste.
One more tip: DON'T drink this stuff with milk and sugar! Certain benefits of tea are lost through the addition of this stuff, especially milk.