dude, you were smart enough to get into Duke and UCSD, and you're here asking a bunch of *premeds* about chances at residencies?
better to e-mail some residency PDs in california and ask them what they think.
my sense is that UCSD, no matter what, is a safer choice. however, it's not so much stronger that you should discount other factors altogether. please don't forget to consider location which is BIG, and curriculum, which is also BIG since you're looking at Duke. hope you're coming to second look weekend!
p.s. i'm not sure that bell knows where/what duke is. location does suck, relative to places like SF, NYC, but not compared to St. Louis, Houston, etc. also, from my firsthand experience, students do work together, a lot. but you know, believing rumors is so much more fun!