United are the best of a very poor lot in my experience (having flown them enough to get Premier frequent flyer status, now lapsed). My experience though is that in general the US airlines are cramped and uncomfortable, frequently badly overbooked (every single time I flew United LGW to the US, regardless of destination, they were so badly overbooked that they were handing every passenger a photocopied sheet offering incentives to take a later flight), poor service (unfriendly, lazy cabin staff - on one United 777 flight across the Atlantic I saw 6 or 8 stewardess call lights, my own included, lit up for a period of 45 minutes - and nobody came to check on what potentially could have been 6 or 8 distressed passengers. When I went back to the galley to find out what was up, there were two flight attendants in there - one was stacking a duty free trolley, and the other was playing with a passenger's baby. Neither ever came back to answer the call lights, btw - they just ignored them.
If you want service, take an Asian airline. If you want fairly cheap, and an ulcer, take an American one.