For quality (always among the best) AND consistency (doesn't matter which masseuse you get, they're all well trained) I like Siam Onsen.

Same building as Starbucks in Patpong, on Soi Surawong side. From Sala Daeng BTS, walk through Patpong night market to Soi Surawong, and it's right across the street.

Really, really, really good foot massage.