Best mainstream American beers: Michelob and Miller High Life (NOT MGD or Miller Lite - there is a difference). You'd be surprised how many American bars don't even carry Michelob, yet I'd still call it mainstream.
While I have tasted many other American beers with much smaller names such as Pete's Wicked Ale, I'll stay away from such smaller names.
Among the lesser mainstream, yet very popular, the best American beer is Sam Adams - whatever variety you choose. I prefer stout, but I'd pick their pilsner over any other beer, if offered say in a restaurant.
Beyond the US, among the best are: Australian Sheaf Stout, Singapore's ABC Stout, the above mentioned Sam Smith's Oatmeal Stout, and Guinness.
Budweiser is truly the worst beer in the world (along with plenty of lesser known American brands which could be even worse). I wonder if Bud has much of an overseas market. I'd be surprised to see them making money in say, Europe. But not much surprises me as I get older!
Ugh! Any Mexican beer makes me ill, even the dark ones!
Roadtoad: you've opened up a can of worms here. There are way too many preferences of taste to accomplish any sort of "scientific input" in the matter!!
