It's a really interesting question. In of itself, I kind of agree with it too- I think depression does often go with intelligence.
Weirdly, I would go for being smart and depressed. I guess it's that whole 'stick with what you know.' Not the smart bit- the melancholy/ depressed bit. I don't entirely trust the 'happy' emotion either and I think it's dangerous to be a fool in this world. My cynicism is what prevents me being utterly exploited. Of course, maybe you'd be happy to be exploited but, it just seems kind of weird to be that happy in this world in a way!
Generally though, it's always tricky imagining yourself as a completely different person. I've had a pessimism/ cynicism about me for a long time. I can't imagine living life without questioning things. I can't imagine being happy just going with the flow. I can't imagine not having ambition and, not being disappointed when I didn't achieve things.
I have known people like that. Not to say they were stupid fools. They probably just had different priorities in life and they did at least seem happier than me but, it's hard imagining a life with completely different priorities.