It's hard for me to pick a favorite- I like all kinds of teas.
I really like Darjeeling. Earl Grey is good, too.
But I also like a lot of Japanese teas. Sencha is a good green tea. There's also Genmaicha, which is green tea with roasted brown rice. Roasted barley tea,Mugicha, doesn't contain caffeine. It's very refreshing iced on hot days.