Building by far, but only if you are capable of doing so. The newest processors are pretty hard to put into socket for newbies, and you don't wanna screw your new intel (AMD is just no). You will need to have some knowledge about parts if you are about to do it yourself. I myself have been building PCs for years, but since I've lost my touch, I'm having friend choose and build it nowdays.
MY HYPE LIST: 1) Gran Turismo 5; 2) Civilization V; 3) Starcraft II; 4) The Last Guardian; 5) Metal Gear Solid: Rising