I'm from Mexico and I've been to Puerto Vallarta many times (my family owns a beach house in Guayabitos, 40 minutes from there).
Is it one of the most beautiful beaches in Mexico? nope. The beach is huge, has many rocks, and the sand is very ordinary. Cancun is better by FAR. The sand is white and the sea has a gorgeous shade of blue. It's more expensive, but it's worth it. There are mayan ruins all across the Yucatan Peninsula... something you won't find in Puerto Vallarta.
I don't know when you plan to visit, but the best time to visit Puerto Vallarta is on Spring Break, it gets wild, with tons of americans and europeans who do crazy things, because they're aware noone knows them here.
Mexican girls also party, but unless you hang out with hookers, I doubt you'll be lucky to score a one-night-stand.
