Hong Kong pop music used to be good during the 70s and 80s; afterwards it was trash. I put the watershed at 1992, the year when Aaron Kwok and Charlie Yeung appeared -- this is when local companies realised that trash could sell.
Taiwan used to have a good tradition of folk/folkish singers who graced the music scene -- always enjoy Chi Yi -- although in recent years you'll more likely find trashy faux-R&B music.
Mainland China has been infected with faux-R&B since day 1 and the market is strongly hype-driven (the "internet singers" craze circa 2006 flooded the whole China with talentless hacks). Unless you're ready to go underground, don't bother.
Edited by FalconP - 7/7/11 at 1:43am