My favorite would have to be Dwarf Fortress. Minecraft comes in at a very close second. They're more of a tie really, it depends what mood I'm in at the moment. If I want to play in a survivalist fashion, DF beats the crap out of MC. If I just want to be creative and build whatever pops into my head, I gotta go with Minecraft. Plus MC has redstone, which is a huge passion of mine.