I've been giving this 'favourite beer' thing some serious thought and I think it just comes down to variety. I really enjoyed the Efes when I was in Istanbul, when I'm in Germany I'll usually have Weizenbier or Hefebier, in Switzerland I usually have Calanda (although I enjoy it less now that they have been annexed by Heineken), in France I've had a couple of very nice beers from local micro-breweries, and here at home I just have one of five or six favourites depending on the situation. Jupiler, Westmalle, Leffe, Lindemans, De Koninck, Palm.