Beer taste

My experience with beer is limited, since I'm only 21. But I've found that my opinion of certain beers is almost entirely based on the aftertaste. Certain beers have a sour, bitter aftertaste (at least to me) that makes them unbearable. I don't know if it's the barley, or the malt, or the hops, but I wish I knew which beers were going to be unpleasant before I ordered them! Here's a quickie list of beers I like and don't like; if you know a lot about beer, please help me!

Good beers:
Guinness
Killian's
Heineken
Big Red (available at Mr. B's)

Bad beers:
Sam Adams
Michelob Lager

If I go by Zesty's beer-drinker classification, then I'm a "Faux Sophisticatous". But pickier.