Rainbow 4 and 5 usually are quite alright, me thinks. Depends on which night of the week and whether there are loads of customers, especially mainlanders. They will otherwise try to trick you into ordering double ladies drink instead of just one.
Also, since when did the Rainbow at the corner of the ground floor become a post-op ladyboy joint. I went in and unexpectedly there was some kind of show and then very soon I realised it was all post-op ladyboys. At least they were nice about it and did not coerce you to sit one down. I left after a beer (massive 185 baht, hahaha), and told the mamasan the show was "nice"