What's the difference between a commuter and a hybrid? In SF, I've seen people commute on road bikes, hybrids, full suspension bike complete with XT bling, etc. I commute on a Trek 7.5FX which is considered a "performance hybrid" equipped with 700x32 tires and mountain bike components. I commute through SF riding 8.5 mi each way from Financial District to Sunset.

I'm sure road bikes are quicker over long distances and maybe climbing , but in SF, it really doesn't matter. In urban environment, you ride about 500 to 1000 ft between stop signs and or lights so there isn't too much advantage to a road bike IMO.

Go to a few different shops and try out different bikes. The best bike will be the one that you will ride rather than leave in the garage/basement/apartment.

BTW, stay off the sidewalks; there are only a few places where bicycles are not prohibited on the sidewalk.