I've been UA Gold for a while as my company had super advantageous fares with UA and despite my best routing efforts to fly OW, I ended up flying UA a lot.

My take is that the app is better, miles never expire and the ground offering is great especially if you have access to Polaris lounges. A very consistent experience across the US and a good one (a part from when the lounge is massively overcrowded).

The planes however....omg....super old. Noisy, dry and with a poor onboard service. Overall, I still prefer BA/AA although I see the allure of going full UA if you are LHR based and travel mostly to the US and want to redeem miles for US flights or DACH/PT destinations.