Well that depends on the style of beer.
In terms of IPA (my favourite style) it would be Epic Hop Zombie.
For the stout end of the spectrum I would have to say a four way tie between Wigram Czar Imperial Stout, Moa Imperial Stout, 8-Wired iStout and Renaissance Craftsman Oatmeal Chocolate Stout. You might notice I like imperial stouts.
I am a huge craft beer fan. Mostly from New Zealand as that is what is easy to get here. Some of my favourite NZ breweries are: Epic (the best IPAs), Wigram, 8-Wired, Deep Creek (my local brew-pub), Hallertau, Renaissance and Moa.
I recently got to try an imported bottle of Rogue Yellow Snow IPA from the US. Brilliant beer. Not quite my favourite IPA but pretty close.