If you don't get a lot of bites here, you could try the forums at motifator.com. I don't think many of the regulars here have a Yamaha in the Motif series.
As for which type of sound is best, what genres are you trying to play in? I play the B3 with my Nord Stage, which has a really accurate B3 emulation and lets me control the drawbars, chorus/vibrato settings, leslie speed, and such, just as I could on a real B3. So even if I can't point you in the right direction for the Motif, I can at least talk about drawbar positions for the genres you're interested in.
Something you could try, since I think the Motif XS has sampling capabilities, is downloading a good B3 virtual instrument, maybe the Native Instruments B4-II demo, and sampling the organ sounds that you want if the Motif doesn't have anything that suits your needs.