Hi all. I need some advice from other traveling locals. I'm an elite member on the United Airlines frequent flyer program, but because of changes due to the merger, I'm considering a change...

Some background. I travel an intermediate amount of miles a year (25k-50k) mostly for work. I initially picked UA because:
1) Only UA uses SFO as a hub, so are were more direct flights to more destinations
2) Economy Plus seating at a low frequent flyer level
3) The occasional complimentary upgrade to first class

Are there any other airlines that
1) Fly a reasonable number of places from SFO
2) Allow access to premium seats (i.e. exit rows) at a low frequent flyer level
3) Allow complimentary upgrades to at a low frequent flyer level

Thanks for the suggestions!