This isn't science or math where you can prove one thing is right and the other wrong; or in this case, one is better than the other. Like many have said, it depends.

Why not seed the discussion of what's more important to you? and what you care about?

Just to help you out, I prefer AA because having flown UA, I find the people on UA to be less friendly. I like the experience of not being snapped at.

SWUs on UA can't be used on the cheapest fare. I purchase tickets with my own personal hard-earned (or not hard-earned ) money, so I want to be able to upgrade on the lowest fare.

I don't care if UA/CO have a bigger network, because I can accommodate with the other OW partners. I'll just fly to parts that they fly to. I'm not THAT picky. Traveling is fun for me.