Just want to add a little note on housing options at each school (if this is a big factor to you):
UCLA: Most M1/M2 students live in a brand spanking new apartment complex that's about a 10 minute walk to the med school campus. This also means that it's located down the street from the center of Westwood Village, complete with a movie theater, hookah bar, good restaurant, etc. Want more? Rent is pretty damn cheap (~$900/ month for a 2 bed/2 bathroom, I think) considering the location in Westwood.
UCSF: They also have a brand new apartment complex for students at the Mission Bay campus. However, the campus is a good 20-30 min drive from the med campus (there's a shuttle that runs throughout the day). While Mission Bay has a sweet new gym & research facilities closeby, that's about all that it offers; the rest of the area is fairly dead. I think they're still developing the area, but right now, there isn't much to do closeby. Also, the rent is upwards of $1000/mo.
You can also live in an older apartment right by the med school campus, but those tend to be more expensive & smaller.
Hope this helps some lucky bastard that has to decide between these 2 great schools 😎