If one is constantly approached by guys , then I would assume that they are more outgoing , friendly , bubbly. Some of the girls may be average looking but those other positive qualities make them more approachable. The not so pretty girls usually put in more effort to attract guys so more guys will approach them.
There is probably a correlation between that and what kind of guys will hit on you.
I think most guys subconsciously go for the girl that looks the most vulnerable.
Beauty depends on whose judging. Personally I'm not a big fan of large breasts, blond hair, ultra curvy, ect - that whole look. Where as some guys may think that's the peak of beauty, I personally find it to be a tad too cliche and uninteresting.
If you're attractive, guys will constantly hit on you. This happens to some of my friends who I think are seriously good looking. One of my friends is a model and the stories she comes out with...haha. If you're hit on often take it as a compliment.
I think it's a mixture, I've noticed guys tend to care A LOT more than we think about personality and confidence, of course they look at beauty too, just like we do but it's not the only determining factor.