Trip7 you are def. correct about the South American women . Central America has a honey hole for women too, its called Costa Rica. CR is my favorite because you pretty much have your pick on what country you want your girl from, the place is a melting pot of women from all over the world, especially S. America.
If you wanna go to Mexico I would say Playa De Carmen or Cozumel. Both are party places with tons to do, but they have a much more upscale crowd that goes there compared to Cancun, plus alot cleaner. If your going down with your girlfriend I would take her to Playa De Carmen a super nice place and the women really like it, every girl I've ever brought down there thaught it was the best vacation ever. Like the one post above said If you have problems flying into Cancun because of flights being full from Spring Break, Fly into Cozumel and take the ferry over plus its a cool thing to do anyway. Almost all of the hotels in Playa are pretty nice the Place I always go to is called the REEF Resort, awesome place at a good price. They are a full service resort for about 100 bucks a night and you can get better prices form one of the travel websites, you cant go wrong with this place its awesome. They are right on the beach, Four star rooms, all meals are included, all the booze you can drink, I would compare it to like a Sandals type of place except you dont have to be with someone to stay there. Good Luck and Have Fun.