Ehh, I don't think I have a singular favorite. I do tend to have some styles I prefer over others though..
I guess the one that surprised me the most, gave the best flavor balance, and biggest amount of flavor for moderate ABV content ... would probably be the Wood Aged 1885 Kona from Perrin Brewery just outside Grand Rapids in Michigan.
However, I would probably say I like KBS better since the KBS is a bit "bigger" in flavor.
But it's not fair to compare the two directly as the Kona was more or less a one time batch ... and the KBS is released every year.
On the other hand, oldies but goodies, like Rogue Chocolate stout continue to tickle my taste buds in just the right ways ...
And then there is New Glarus Wisconsin Belgian Red, which hits like a wall of sweet, sour, and tart cherry. It's not particularly complex, but, it is just so amazingly tasty I don't care!
That said, day to day, I'm rather fond of any Lambic, Stout, Saison, or Gose.