At places where I know I can get a good draw -- the kind where you have to wait five minutes before it's ready -- (which are few), I drink Guinness, but never in bottles or cans.

Otherwise, it depends on what the establishment offers. I used to abhor all Mexican beers, but I've found that Negra Modelo is pretty good if forced into a Mexican beer (usually at Mexican restaurants, which seem to offer them and standard American beers, which I never drink).

If I'm going to buy something at the store, I usually just get something I've never heard of before, to expand my horizons.