I've been doing sort of the opposite thing this year, as I status matched from Plat to 75k on AS. I think I'll probably be sticking with UA next year. My flights on AS have been great, and upgrades are waaaay easier, but it's not great flying them out of SFO. Besides the fact that there's no AS lounge available when flying domestic in SFO, I pretty much always have to connect in SEA. SFO-SEA is a short flight, so it bears the brunt of delays when SFO has the dreaded CLOUDS AND FOG. If I then miss my connection, there aren't a lot of options for rebooking, and I have to stand in line at the tiny customer service counter. The ability to SDC for free in the app is really the best thing about UA for me, that added flexibility makes all the difference. Those factors might not be as important out of PDX, but something to consider.

The tl;dr : AS is a better in flight product, UA is better for scheduling flexibility