River Oaks is a fairly nice apartment complex. It's a gated complex and it is within walking distance to Tower Market, Starbucks, and Quiznos. I know you said you don't have kids right now, but if that should change, it's right across the street from Yuba City Charter School (for now anyway--I think they may be changing locations though) which is a GREAT school that my kids went to when we lived there. As far as neighborhoods go, the Bogue/Garden/Railroad area is okay. The neighborhood around Lincoln school (Lincoln & Walton) is a nice area as is the Happy Park area. NW Yuba City around the Regency park area is okay. Sutter is nice. Areas that I would avoid would be anywhere along and off of Percy Avenue, anywhere close to the Fairgrounds and Gauche park, and the Clark/Queens area. There are a LOT of apartment complexes off of Gray Avenue in the Casita/Kenny/Melton Drive area that I would definitely avoid--lots of gang activity over there.
I was born in Yuba City and lived there for the first 30 years of my life....we've been in Nebraska now for 8 years and I like it so much better here

Good luck in YC though. One good thing about YC is that you are only a short distance from so many things, Sacramento, Reno, SF, etc.