I fly Delta as my backup... problem is Alaska failed at taking me so many places this year I ended up flying more Delta (Toronto, Montreal, Mexico City, etc).
I try to fly directs as much as possible, and prioritized in the following order:
Alaska (Gold for 2020)
Delta (Platinum for 2020)
United (Silver 2020, thanks to Marriott)
I might go all Delta next year because Diamond is likely better than this split status thing I have.