I think a little bit of makeup generally looks the best -- not an excessive amount, but just some cover up and maybe eyeliner and mascara. A natural look. If you look at a girl and assume she's not wearing much makeup (if any at all) then she's doing it right.
No, I think that women can look beautiful without make up, so don't think I'm saying that everyone should wear make up but when applied properly (the right shades, shapes etc. for each completion and face shape and used to accentuate the best features and cover or hide some "less desirable" ones) I think anybody would look better.
Every girl is more attractive if they can apply make up professionally, and only enough to highlight her features, but avoid looking "fake". But if she is bad at putting on makeup and looks like a cheap whore, than we would rather you wear no makeup at all.
But it all comes down to your actual attractiveness. If you are already attractive, makeup will make you even more attractive (if used correctly). But if you are unattractive, make up won't help.