Both UA and Alaska can get you from SFO to any of the Washington DC area airports nonstop. United will clearly have more flights per day, so I'd start off with looking at the Alaska schedule and see if their service works for you. Using BWI as an example, which always seems to have the cheaper fares than IAD/DCA, there is only one flight per day in the morning and one flight back in early evening. There are morning nonstops to both DCA (8am)and IAD (10am). There's a second service to IAD in the afternoon (3:45pm). Coming back to SFO. the only morning nonstop is from IAD (8:20am) with a second flight in the evening (7:10pm). There are also late afternoon/evening nonstops back from BWI (7:15pm) or DCA (5:20pm).

Alaska has basic economy fares that allow a carryon but not seat assignment or fare changes. They tend to run about $60RT less than their regular main cabin fares. Alaska also has a stellar frequent flyer program that awards miles based on distance and elite status. With 40K a year (Gold) you'd get 100% flight miles and 100% bonus miles on cheap economy fares, so around 10,000 miles RT.

I have friends that regularly fly OAK-BWI nonstop on Southwest (7am departure, 2:30pm return). One of them is top tier with the free companion pass.. Don't know much about how they earn miles/points, though. Plenty of other Southwest flight options with connections (as there would be with Alaska via places like PDX, SEA, LAX, SAN if you really wanted to stick with them).

The only nonstops I see OAK-SLC are on Southwest (3) and Delta (2).

Alaska only has one evening nonstop SFO-SLC. Might want to stick with DL or UA on that route.