I've been to most of the lounges in SFO and I think for sheer comfort, service, and selection, the VA Clubhouse is the best. They have a nice made-to-order food menu and the food is actually good, full bar, comfortable seats with good configurations for both groups and single travelers. It's large enough to find a quiet spot and the service is good and attentive.
The biggest drawback with this lounge that it's before security. Which means that you can't fully relax. They do everything they can to make that a smooth experience - they will chaperone you down to security, get you into the priority line (or TSA-Pre), but at that point you're on your own. My experience going through was pretty breezy, but you just don't have the same level of comfort when you know you still have to deal with the unpredictability of security after the lounge - that's the reason I give it 4 stars.