In my experience, the guys I thought were so hot turned out to be complete d-bags personality-wise, which made them less attractive to me physically. Guys I didn't find as attractive physically became more attractive because of their stunning personalities, senses of humor and other traits that I found appealing.
I think extremely good looking people may feel like they don't have to be 'nice' because they can get anything with their looks and are used to that. People who aren't as good looking maybe have to try a little harder and end up being better people because of it. I'm not saying a hot person can't be nice or a less hot person can't be a jerk. I'm just going by my experiences and how I view things through them.
Attitude is everything and there's a fine line between confidence and conceit. Looks matter but personality is more important.