I recently flew with United Airlines. They were £250 cheaper on the LHR-EWR route than BA. I flew with then pre-pandemic and expected a cheap nasty product. The fact that I had an ok flying experience left me pleasantly surprised. Yes, the 767-300 is getting old, but it was clean and the IFE was good. Their staff were for the most part nice and their app is really good. While I would pick BA or Virgin over United if price was not an issue, I would not be upset to have to fly with United on the same route again.
That said, the departure area of Newark Airport was not a nice experience. It reminded me of JFK in on a bad day.