that really is a tough question, at first I picked Europe but then I started to remember some American brews that are absolutely sensational..
but some of my favorite are:
my absolute favorite ale, you Scottish bastards got it right on this one
probably my favorite IPA
probably my favorite lager
and last but not least my favorite from the Boston Brewing Company, winter seasonal ale
edit- the only ale in the trappist style I have tried was the Ommegang, which is actually an American ale styled after the Belgian abbey ales..
Honestly, I was disappointed, didn't like a single thing about it. maybe the real trappist ales are better but I would not buy this stuff ever again.