You say you are mostly going to fly domestic, so here is my take:

I would think about CO seriously. Their upgrade policy is still excellent (esp for the top tier) and they have the Newark hub. Most people like their service. Downsides are in my opinion Northwest and America West. The first I hate and the second I dislike.

You say that CO lacks west coast routes, and this is a problem for you. But I believe they have a partnership with Alaska Air which can somewhat help in this area.

With AA, it seems to me that depending upon where you are going, you'll be seeing ORD and DFW quite a lot. If this is not an issue, it's something to think about. And certainly AA has a decent network on the west coast.

With UA, there are some direct flights but again you'll be in their hubs, ORD or IAD, I would imagine, quite a bit. They have an excellent network on the west coast, albeit it is the sh*ttle.