It seems you fly quite a bit, and on a variety of carriers.

I would wait and see what happens with CO-UA in terms of benefit reciprocity. While your upgrades and US convenience would sway you towards US over CO, if we see some sort of advantage of a CO Elite flying UA, you may want to keep CO status over US. So it's too early to tell.

That said, presently, and all things being equal, US CP has more benefits than CO Plat. You get free standby and same-day confirmed, as well as a couple SWUs.