Completely personal choice of course.
But if it was mine to make it would be the Yeti for a couple of reasons.
Early Yeti's have a relaxed and ride and the most excellent Patco tubing, plus if it is early enough they were CA made (i'm from Cali). Also the frame details scream mountain bike to me, even though they were heavily influenced by BMX designs.
The later Chances were made by Serotta so to me they don't have the coolness factor of the earlier rides. I'm sure the build quaility is still top notch and the ride would be primo.
Another factor, will you be riding rigid or run a sus fork?
Rigid=Yeti
FSus=Chance
Just my opinionated opinion.