It seems like AA is getting the biggest boost from fleeing UA elites in SFO, but personally I don't find the idea of having to connect to get pretty much anywhere at all very palatable. You may want to look at who has direct flights where in order to make that judgment ... the Wikipedia article on SFO has a pretty comprehensive list of flights ...
http://en.wikipedia.org/wiki/San_Fra...d_destinations
Personally, I'd be inclined to use a mix of Virgin America (for destinations that they serve), along with AA.