Czech beer is the best I've had. Ridiculously cheap too, was something like 30p a pint (still sounds ridiculous, I'm wondering if I remember correctly) - in Prague
Germany, I suppose. Very broad variety and tradition (many Bavarian breweries exist since the late middle ages I think )plus the Reinheitsgebot.
I think Germany probably has the best variety. I'm trying to get through all the different styles but some of them are quite hard to come by.
Belgians do the best abbeys, dubbels, trippels, witbiers and lambics, Every beer is slightly different.
Czech does the best lager.
USA has been a serious force in IPAs for a decade or so now, and the UK is definitely up and coming at the moment, however both are still sullied by the difficultly of getting a decent beer in the majority of pubs. The UK is the worst at this.
The USA has a great craft beer scene, and has even invented a few of its own styles such as California Common (aka Steam Beer), American Pale Ale, Cream Ale, plus a few others.
It definitely has to be between the UK and Germany, personally I would say the UK on the basis that there is simply more variety in the British brewing tradition - that said British ales can be an acquired taste and if your palette veers more towards the lager and wheat beer spectrum I can see why you'd pick Germany.
I think Belgium strolls a third. Brewing in the USA is not the joke it once was - there's certainly a greater variety than there once was but they need to learn not to make everything so damn sweet and they lose points for the fact that good beer is still a niche market there, not a standard fact of life as in most of Europe. Therefore the Netherlands, the Czech Republic and Ireland can play off for 4th, 5th and 6th place.