Skyrim. And here's why:
When someone says "best looking" the first thing I think of isn't "oh fuck check out that sexy engine running those amazing uber-detailed images", I think "that level design is beautiful, those areas may be rough but they're visually striking"
And nothing I've played has been as visually striking as Skyrim. Yes, the dungeons were like someone drilled a hole through a shit pile, and yes, the graphics were rough as hell sometimes (spoken from xbox perspective btw, the principle is the same though). But my fondest memory in all of gaming was at one point, I just walked out of a forest and saw this gigantic, amazing plain, with mountains and scattered trees and stars overhead. And the aurora, and the flying dragon in the distance, and the fires of Whiterun burning far away. And I honestly loved it.
