I agree with the advice about the cockpit measurement, I'm 5'3 with a 29.5 inseam, and I have really short arms. I fit a small Santa Cruz Juliana. Here's their sizing index:

http://www.santacruzmtb.com/juliana/...?sizing=1&x=65

I'm really happy with the WSD design, I used to ride an old 15 Schwinn Moab and the Juliana is a much more secure ride, and a MUCH better fit. (I'm actually moving to a WSD fit on a road bike too since I've had such a good experience with the Juliana!)