When are your travel dates? If you are looking a ways ahead, it might be smart to wait a bit.

If it were me, I might spend the extra 83 pounds to have a chance at an upgrade, but really it's kind of a toss-up as you can still get dividend miles if you take the UA flight.

I would probably take the Southwest flight to Oakland. As you said, it's a short flight and it's easy to get to SF from Oakland on the BART. Or, if you really want to have fun, rent a car and drive from LA to SF.