UA for me... AS has lots of non-stops but not much frequency to those dests.
UA requires much connecting in DEN but thats one of the best airports to connect through... ORD or IAH? no way!
You can red-eye to IAD and get to most places in the east coast in the AM. This gets you 4.5 hrs of sleep at least.
E+ rules, no doubt about it. Only 25K miles to hit Premier and have it for free. You can also buy as you go or get E+ access for $299
UA does IAD, ORD, DEN, LAX, SFO, NRT, PDX from SEA.