I'd go with the 35/2 for a general purpose lens for a lightweight, compact kit.
And then the 50/1.2 for a more special purpose kit (portraits, say). But that's only because I much prefer environmental portraits over those tight, neck and face shots. Plus, a 50/1.2 lens covers pretty much all you want to do with a rangefinder - just ask Cartier-Bresson, for whom a 50mm was sufficient 90% of the time.
EDIT: then again, if the 50mm Summarit is the older f1.5 version and not the modern f2.5, I'd take that instead of the Canon. Smaller, lighter and only a half stop difference which on the M9 won't mean much as you can easily jack up ISO. Plus, I prefer the old Summarit's rendition... classical? Yessum!