+1.
There are now Superrich booths at some BTS stations. Asoke has one, but as Lorry said, they offer slightly less than the main ones in the sois opposite the northern end of Central World, to the left of Big C when looking at it.
There is also another place called Vasu that gives pretty decent rates near Nana Soi 3 I think. It's a while since I last went there.
BTW. SuperRichTH and SuperRich have apps so you can check their rates on line on your phone..