Personally, I've always loved bumbling Clark, because, for me, that's the only way I could see the glasses potentially working as a disguise. My favorite version is probably All-Star, where Clark is just this slovenly, clutzy oaf. He's still a competent reporter, but he becomes another person, almost.
Personally, though, I like a combination of the two, and I think it's a lot like Batman, in a way. You have the public persona, the private persona, and the alter ego. Bumbling Clark Kent is the front he puts up for people, while Superman is the embodiment of his Kryptonian heritage/the icon that people look up to, but, ultimately, when he comes home from work and he hangs up the tights, he's a good-natured farmboy from Kansas.
