As my username suggests, so does my recommendation to go Alaska. I've been loyal to them since 1994 and haven't regretted it. While I would love for them to be part of one of the larger alliances (Star, OneWorld or SkyTeam), they have a nice mix of partners all by themselves that fly all over the world. We just booked our second First Class mileage award with them to South Africa (on BA).
We're both MVPs (not Gold) but feel like we get treated very well on every flight. The times we haven't, AS has been there to make sure they've rectified the situation. They do care and will work hard to retain your business.
We have a friend who is an FA for UA, so we always know what's going on there. Still, we prefer Alaska.
As far as WN,
. The only credit I will ever give them is they serve a niche market (Low fare = Low class). I avoid them at all costs, and yes, will pay more to do so. Although, lately, it hasn't been that much more at all. After the two trips in my lifetime on them (both of which should have been listed as violations of human rights), I'll never fly them again. Think of being on a public bus in some remote area of India or China, and that was to me, the inside of WN.
Just my 2cents. Enjoy your flight on Alaska - I'm certain you'll be treated well.