This may be a case of not practicing what I would preach generally, but I would say go for AA's program or UA's program. DL is operationally better for me, but I am no fan of the DL loyalty program despite it being the program in which I earned my first airline elite status. The AA program has the Alaska and Jetblue tie-ins as noted above, and I can still get very good value redeeming AA miles -- something I can't as easily do with DL miles.