I drink everything pretty fast. Doesn't really matter whether it’s milk, water, beer, or a Tom Collins. If you’re a server at my table in a restaurant, don't bother asking—yes, I would like more to drink, thanks.
There's no beverage I drink faster—nay, chug—quite like unsweetened iced tea. I know it’s better for me to drink unsweetened tea anyway, but I just happen to like the taste. It’s what I want the most after mowing the lawn (even more than a High Life or a good kölsch). I can drain a quart of unsweetened tea in under 10 seconds if I'm truly thirsty.
I'm not picky about the brand/variety when I'm thirsty, but given the choice, I like Japanese teas - they tend to be more earthy and vegetal than Western palates prefer, but they tend to quench my thirst a bit more effectively. Ito En is a solid, common brand I see at ramen shops and Asian groceries, and my office has been carrying some of their teas in our beverage cooler for some time now.
One of my increasingly favorite products is the Ice-Steeped Cold Brew green tea. It's milder than some of the other products (not that I mind) and has a little less caffeine (that I do mind just a little :-P), but what strikes me the most is the aroma. The taste is in line with the above, generalized description, but this tea has a strong, uncanny aroma of honey. Bottle after bottle. It's intoxicatingly sweet-smelling, and provides a nice contrast to the flavor profile. This isn't sponsored (as if...), I just love the stuff. If you like unsweetened tea, find it. And give it a sniff!