Ive always had a good time in Phuket because it's a bit smaller and I've had one of the best experiences ever with a girl I picked out of a club there late one night. Places like Pattaya I find overwhelming for choice and the girls there are super pushy and sometimes lazy.
BKK is always fun but hectic - I've had some great adventures there too, particularly in and around Nana plaza. I like the freelance girls that hang out in the surrounding bars - always a great night out and lots of nice attractive WGs to be had