Intelligence matters and so does personality. But looks matter most.
It's from my personal experience and my observation of the people around me. I was stick-thin throughout middle/high school years. I was extremely insecure and jealous, I had little to no confidence. Yet, guys approached/chased after me wherever I went. I was that "popular" girl. All my friends were skinny and many of them weren't kind or nice but were hot and popular.
Then college hit me and I gained 50 pounds. Guys suddenly stopped talking to me. I had to initiate conversations to make friends. The only places where guys would approach me were bars and clubs. I was nicer; I was way more compassionate and confident. Yet it didn't matter because guys didn't bother talking to me and trying to get to know me.
Now I lost all the weight and am popular again. And I honestly don't think my nicer personality has anything to do with it. When you're pretty, you can get away with a lot more things than non-pretty people do. I'm still a bit jealous and possessive. And guys find it cute or they even say they like it, though they were like "ugh, stop being clingy" when I was heavy.
Looks matter most because people don't even give you a chance to show your personality if you aren't good-looking enough. And it's not just about girls but guys too. Seeing them going after douche bags and ignoring all those nice guys confirms it.
Things might be different for older people but I think it's pretty accurate for teenagers and 20something.