Sorry, which Massage Parlour Attendants comparison did I miss?
I couldn't say as to ethnic staffing, but, to my taste decor was equally uninspired at both. At Diamond you use one of a pair of common adjoining shower stalls, which is only nice when one of the MPAs uses it too. All too rare, sadly. Diamond is showing more wear, but is clean where it counts.
Bottom line: nothing at S9 had enough pull to draw me back, but I've repeated often at Diamond with several of the MPAs without encountering one I'd pass on for next time.
Trouble is, as we all know, it's the second and subsequent visits that are the real pleasures and the real test of quality time. The first is never a true indicator. So maybe the MPA at S9 would have been stellar next time, but I doubt I'll ever know.
Can't see you'll go far wrong either way, you'll owe yourself a second visit with the lady, and in in the spirit of research I can't see how you can not check out the other place. Enjoy.