You missed Delta JFK-BOS. Delta still has 500-mile minimum for each segment. This goes for general members as well as elites. IIRC, only elites on UA get the 500 min but I don't follow UA very closely so I could be wrong. (IOW, please, people, don't flame on me just correct me if I am wrong)

While Jet Blue has really great coach the flight is really too short IMHO to value the TV. They also base their FF program on $ spent not distance flown.

While Marriott is running a pretty good DL promo right now, Delta is much more in bed with Hilton. They run numerous promos throughout the year and even promos where Hilton stays can earn elite qualification miles with DL.

Since you will also be going NYC-SEA I would definitely give DL a look. They are very generous with upgrades for the top elites and you would get to Diamond in no time based on your OP. Their soft product coast-to-coast is pretty good. (oh man, did I just open a can of worms)