I was just there in december. If you stay in "regular" San Juan then stay either on the beach of as close to the beach as possible. Its all very americanized there with the stores and shyt (Walgreens, McDonalds, BK, Popeyes) and you use American money for everything. If you plan on going all around to different places, then rent a whip. Cabs are everywhere but you will find yourself spending $20-25 for cabs randomly. Also, if you get a whip, they sell gas by the liter out there, so the shyt comes out to like $5 bucks a gallon for gas.
The beaches are official, but if you are in "regular" San Juan, get used to seeing planes take off every 10 minutes. But you get used to it after a while. There will be Americans everywhere in San Juan and its like a budget ass version of Miami out there. Many of the hotels have casinos in them and are within walking distance of each other.
Old San Juan is official but VERY tourist oriented yet still retains its old school charm. A good history lesson if youre into that kind of thing. If you go to Old San Juan, be careful about rollin into La Perla, which you will notice, since its by the old castle looking fort. La Perla gets turn the fukk up and they will know you are an outsider immediately
Hit up the rain forest, which is a 30-40 min drive from the beach at San Juan. That shyt is a once in a lifetime kind of thing and you'll have mad fun walking the trails. You can pay someone to show you around the rainforest or just go by yourself in a car if you rent one.
Alot of the resorts have their own clubs, so if you stay in one, you wont have to go very far to get your party one.