My favorite (go with the flow...) is the 777, for its spacious feel. UA also has video screens in the back of their 767 coach (at least international DUS-ORD-DUS), it is a nice feature, but the 777 feels more spacious. Since I fly coach a lot, that's my main concern. The 737-500/600 can be fairly nice if new and if you don't have to fly them for longer than 1 1/2 hours. Biz/First on the 747 has received high marks, but IMHO in coach the 777 beats the 747 by far.