As a side note, welcome to Boston! And I highly recommend taking the T into the airport. Least that way you don't have to worry as much about traffic.

Personally I find that since no one is really all that strong at BOS, I can fly whomever makes the most sense. I tend to stick to UA though since mostly I fly to the west coast and can do so non-stop with UA. NW has decent flight times out of BOS, but not so great into. (Last flight out is at 6pm, last flight in is at 10pm).