What is the best beer ever?

Taste is a subjective thing. The type of beer you like will help determine what you think the best American beer is. If you go by sales volume Bud Light is the best American beer, it is certainly the best selling American beer.

If you are going by flavor profile and hype surrounding a beer then you will come up with a different answer.

Beer Advocate (One of the top two beer rating sites on the internet) shows Pliny the Elder by Russian River brewing (California), an American Imperial IPA, as being the top rated American beer.

Rate Beer (the other of the top two beer rating sites on the internet) shows Oak Aged Dark Lord by Three Floyds Brewing (Indiana), an Imperial Stout as being the top rated American beer.