The herbal teas have suggested health benefits, according to what's in them. Camomile, peppermint, fennel, etc. are used to calm a dodgy tummy, as a diet aid and whatnot. I don't know whether there's any scientific fact behind it, but some people say it does work.
I don't think there are any particular benefits to fruity teas, but they taste nice, add to your fluid intake and also, I find drinking hot water has an *ahem* flushing effect on my system!
I also drink green tea, which does the same thing. That reportedly is a good slimming aid as it may help speed up your metabolism and I find it is a very good appetite suppressant. If I have a cup mid-morning, I usually don't get hungry until 1pm-ish instead of midday on the dot!