As an ex US1, now CO Plat (never held both except during my status match year) I will not deny that EUAs are plentiful on US and hit or miss on CO. And when you're in back on CO, it's a nice reality check that flying can be a miserable experience. However, I found US to be completely unreliable. I don't care if I got the upgrade if they can't get me to where I need to be when I need to be there.

I'd hold off on doing any matches until you figure out what the agreement will be between UA and CO. It might be better go split your allegiance between two networks.

It's really hard to answer your question without knowing your flying patterns. As a NYC based FF if I flew primarily domestic, as much as you apparently do, I'd split between CO and DL once CO joins Star.