Just keep in mind, that more partners does not a better alliance make. It really comes down to where u want to fly. Carefully consider the various alliances. And again, remember that there can be partnerships outside a particular alliance.

So look at the various airlines and see where they fly and how often.

For myself, I am based in Chicago and do mostly mid-con flights. United just makes sense. Particularly since I will soon be based in San Francisco.

You mentioned, however, that you want to go to Alaska. In that instance, you might consider airlines Alaska Airlines is partnered with. After all, when it comes time to getting an award ticket, it will be much easier to snag a seat on an airline that serves your destination far more then, say, United.

Again, just keep in mind your own travel plans and where you would like to go. You don't necessarily need an alliance with 18+ partners.