If your in to the more muscular type, I would avoid Sunee plaza are where they are more fem, small & sometimes probably under age.
Check out the main Boyz Town bars especialy Wild West, Copa & Boyz Boyz Boyz they all have a good range of better built guys. During the day you could also try out Jomtian beach (the gay beach) a lot of the well built guys enjoy hanging arround there and are generaly very keen talk etc.......
Some of the Muay Thai boxing bars on Beach Road can be good fun, the fighters come to any western guests (or probably anyone who could be a tourist!) after each fight, in the hope of a tip, I have ended up then chatting and getting to know a great young fighter on a previous visit.
Later at night a lot of the boys who have not found a new "friend" for the evening head to some of the late night clubs, you also find a lot of the more athletic dancers in these places are pretty availible! The clubs appear to change every time I visit, Hollywood used to be good, last time I was there Dude was OK as was X Ray, the free gay mags offer pleanty of info, as do loads of other postings on this site.
Dont know Chiang Mai, but pretty certain you will find what your looking for in Pattaya - enjoy!