Too late to help for this flight, but I agree with everybody else on Alaska over United.

Alaska and United are my two primary airlines - UA has preferred carrier status for my business travel, so they usually, but not always, end up cheaper for transcon work travel. I fly mostly full transcons for work and for some destinations (IAD) I fly united because they have a lot of flights to choose from so I can change flights and get home faster if I finish early and can find available seats home if things are delayed. I fly AS mostly north south along the west coast for personal travel, where AS has lots of nonstops, and has flights out of BUR, which is much nicer than LAX. Unlike a lot of posters here, I've generally had good experiences with UA crews and gate staff, but in my limited experience (only a year) with AS, they do come across as actively friendlier. Part of that is probably related to supporting a smaller network and dealing with fewer passengers (and fewer irrops). I won't fly UA without E+ anymore, but AS has generally been more comfortable in the back of the bus without having earned status, which I just got this year.