Hands down the Anatolian Shepherd. Huge, fiercely loyal and protective, no common genetic problems and long lived for a large breed to boot. I mean if a dog won't kill or die for you why feed it?
I'll formally inherit my aged aunt's rescue shepard/chow mix this weekend, so for now, rescue shepard/chow mix is my favorite breed. However, for pure breed I love labs (especially yellows like my Jack was). Someday, I want two standard poodles.