For everyday OC, a level II is sufficient. Level III would be a bit much, I feel. However, a level III would be a better option if you're going to OC in a large crowd. Most people here carry some kind of level II system. The level II Serpa is common, as is a leather holster with a thumb break.
I don't have any personal experience with the Safariland holsters, although I hear that they are a great choice. I use the Blackhawk Serpa CQC level II, and I love it.