lots of bikefolk in potrero hill/mission, but a route called "the wiggle" winds its way through the city up toward the panhandle. i bike from 8th ave (near UCSF) to Sausalito for work, and only encounter 2 hills. it depends upon what you're looking for; i always see cyclists in the headlands, but would likely never attempt those hills for laziness.

Anywhere on the lower peninsula near Highway 280 so that you have access to the Santa Cruz Mountains (unless you don't like to climb of course)

One favorite spot for cyclists around the bay area is Marin County. I have not lived there before but included a link where you might be able to learn more

I would highly recommend living next to a GREAT spinning center, i.e., gym. If you are more of an outdoor person, any location that has good access to south (Skyline = 35) or north to Golden Gate Bridge is good. That would include, all locations near Golden Gate Park/Golden Gate Bridge, Marina or near Ocean Beach.

The Richmond or Sunset districts are great for access to biking venues (not the best weather-wise, tho) - you can easily get to: Golden Gate Park, The Presidio and the Golden Gate Bridge (for rides to Marin County). On certain evenings, I believe there are still some serious riders jamming through GG Park doing laps at top speed - you can join them if you can keep up with them!