Depends on who is paying, how important non-stops are and how flexible timing is. UA will have the most non-stops and choices, but be most expensive (IAD hub). AS can be very pricey transcon and does nothing for East Coast. US, DL, AA and CO will probably offer cheaper, longer, indirect options. I'd avoid NW. NW is so dysfunctional it's hard to believe they will last out the year.