Not at Davis now, but graduated undergrad there in '01. I don't see how its changed much. Here's the deal, at least when I was there:
W. Sac: can be pretty sketch. I never spent much time there, but from what I know, it has some pretty shady areas. Its kind of an industrial type area: lots of industrial parks, the Port of Sacramento, etc. are there. Also, the commute into Davis can get interesting in the morning if there's an accident on the Yolo Causeway. But if the traffic is good, the commute is probably 15-20 minutes. On the other hand, it splits the difference between Davis, where the med school is, and Sac, where the hospital is.
Dixon: Never actually been there, but probably a decent place to live. The only downside to it I can see is that its west of Davis on I-80 (read: farther from Sac and UCDMC). Probably a 20 minute commute on I-80.
Woodland: Has good and bad areas. Not sure what areas of town the any of the apartments are in. Probably the best place to live if you want to commute to Davis. You just get on Hwy. 113, which at least when I was there almost never had traffic problems and 15-20 minutes later, you're there.