I suppose a first time visitor should check out Bangkok, if only to get it out of the way. Sure isn't much to bring you back though. Pattaya = party town. Phuket = the standard resort crowd mainly. Phangnan = the 'look at me I'm a cool backpacker' crowd.

Which you prefer is down to you.

Don't try to do too much. When you are back on the plane going home the last thing you want to be thinking about is all the wasted time spent on planes, trains and automobiles.

A couple of nights in Bangkok is ok. Stay near the nightlife then hit Pattaya. Perhaps give yourself options for the last couple of days.