Jaco is pretty much the best place in costa rica IMO, but manuel antonio is very nice as well, theres monkeys everywhere. Id recommend si como no for a nice hotel there
http://www.sicomono.com/. Quepos is near by and has some nightclubs or theres a huge party on the beach in manuel anotnio every fri sat nights.
There is also an airport in quepos so you can get back to san jose for like 75 bucks instead of the 4-5 hour drive.