I was UA 1K for years. I liked the First class service, and I like the multi-zone boarding. As a US CP I have to battle with the rest of the Plat, Gold, Silver, Zone 1 herd. On UA I had a specific 1K boarding and did not have to wade through the herd.
I have written US about breaking up the boarding process into more zones.
I do however notice US on time percentage is waaaaay better than UA. Also note that I have not flown any cross-country US trips, only shorter hub-to-hub's, so the service is probably better on longer hauls, I just haven't had the chance to experience that yet.