That's pretty subjective.
I'm a big fan of Amber beers. Dos Equis ranks pretty high with me where "common" or "easy to find" beers are concerned.
I like Bass quite a bit.
I'm a big fan of Anchor Steam. It's got a weird bitter taste that is oddly tasty. It really messes me up though.
Pete's used to have a Wicked Winter Brew that was good. It was seasonal. They don't make it anymore (since '96 I think).
I like Hefeweizen. Blue Moon is great. But one must recognize that Hefeweizen is a beer for people who don't drink beer. Kind of the wine cooler of beers.
Best of the best? Hmmm.... I'd have to say that the best I ever had was an amber that a guy I knew used to brew himself. He made ALOT of it. Like WAAAYYY more than he was legally allowed. He was a true brew master. His name was Mick. He had quite a few firearms too as I recall, and had a penchant for shooting at random times, at random things, off his back porch. Pfff. Haven't seen him in almost two decades.
Alot of beers I've tried that rank very high I can't remember the names. I'm always with people, usually distracted, later on drunk, and they're usually pretty uncommon and hard to find. More times than not though, I remember them when I see them.
Worst of the worst? Three way tie. Mickey's, Grolsch, and Keystone. Although, if forced to drink one of the three, I'd take the Keystone. I'd voluntarily smooch a skunks a__ before I'd drink the other two. Then I'd wash out the taste with mixture of Colt 45 and Old English.