One that doesn't put you into caloric surplus week in week out. (provided your mission isn't to gain!) Define looking good though, staying lean? Getting bigger?
Over the last 12 years I have found a diet consisting of roughly 40% pro, 40% cho and 20% fat has been sustainable, allow me to go out, enjoy myself and still maintain a good physique. Of course, if I want to get leaner, I have to tighten the reigns substantially. I have found that it's best not to gain too much weight when "bulking". I see people gaining 20kg over the course of a year and think, yeah, that's not helping. And, it's definitely not all LBM.