I'd recommend Csi Mini Storage! I used the Richmond location for about a year before I moved. Their service was good, and the guy there was always helpful. I had to get a lock cut off one time, they jumped right on that. They weren't the least expensive, but they weren't the most expensive either.

The facility was clean, and I felt safe there. The container was high quality, and the location was convenient from both Marin and the East Bay.