I think it's a combination of both...and I think it's also important to understand the difference between what makes someone pretty, and what makes someone attractive.
IMHO, there are certain things that are universally agreed that makes someone pretty. These may include things like good facial symmetry / proportions; good clear healthy skin; a nice smile; button nose; cheekbones; a good physique etc. How pretty someone is (or handsome for guys) depends on how many of these things they have and how well they radiate them.
On the other hand, (IMHO) attractiveness, is more to do with how you present yourself. This includes how you dress and carry yourself; how you wear your hair / make up; your overall vibe etc.
Personally, I think there's not much you can do about how pretty you are (unless you've got some spare cash, and you know a good plastic surgeon)... but anyone can make themselves look attractive, with a bit of help / guidance if they really wanted to.
I know it's a bone of contention here, but the other thing to bear in mind is the whole league malarkey. With those who are "stunners" (i.e. those who have a large quantity of both the pretty and attractive attributes), they will be noticed by most people they meet (well the ones who aren't blind at least lol). However, when it comes to more average people, most will be indifferent... but to those who go for whatever "type" the average person is, they will obviously stand out to them more.