I've been a longtime CO BF user, and recently have been mixing up UA business flights.

CO business is definitely a bit better, traveling alone, I like the divider between the seats. As long as you are on a co 777 or 757 you have new seat which is similar to UA as far as comfort. CO has much more storage and useful spaces however then UA, and the meal service is far better.

I have only been booking UA flights when i have hopes of upgrading to 1st using miles, otherwise i stick with CO. And even UA 1st is only slightly better than CO BF, but even in UA 1st, the meal is better in CO BF.