Different people have different needs are you're aware.

For the traveller who doesn't travel too much, Alaska is a good program because you can fly AA, CO, DL, NW, and some other airlines and get credit. However, you'll forfeit some upgrading and online bonus miles (which have been reduced or eliminated on some airlines).

If one travels a lot on a specific route, one airline may offer a better schedule. While schedules are subject to change, often they don't change too much. So a later Friday flight may be the one for you.

Southwest's product has remained fairly stable for years while other airlines have gotten worse to the point that WN no longer stinks. Their ff program is great for basic transportation (i.e. domestic coach seat) because they have very good availability. I may have a 100% success rate in getting requested awards versus approx 5% with United (your experience may vary).

When I was a NW gold level, I got upgrades very often. DL gold is not quite as good, but not bad, and about the same as CO gold. Now, I don't spread myself so thin and dump all the Skyteam miles into one airline.