I used to go there fairly often for work, but it's been a long time. Always stayed in the same place, which I think is called Condado Beach. Couple of big hotels and casinos were there....nice area, tons of nightlife.
The bus to Old San Juan was a quarter...not sure if it still is. Those bus drivers will scare the hell out of you, but it's still better than driving yourself.
I rented a car there once and turned it back in as soon as I got to the hotel. Not really a place you'll enjoy driving.