It depends. I don't usually like black teas, but there's this one with ginger that I really like. I drink it with milk and sugar. Green, white and oolong teas I will either drink with or without sugar, depending on the overall flavour, but never milk. I happen to like some of the grassier tasting green teas without sugar, for example. Chai tea, with spices and stuff, tastes best with milk and sugar.
If there are sweets and/or pastries available, then that just makes it better.
EDIT: Though it really doesn't count, I sometimes drink those canned iced tea drink if I just need a quick beverage. I prefer real tea, but it sometimes takes too long to make.