A bunch of reasons.
- My regular travel destinations include MSP and DTW, so frequent nonstops are nice to have
- Selection of flights out of BOS
- Very good IRROPS handling (and I don't think it's all because I'm PM)
- Amex MQMs mean I can usually bump up one level of status
- Efficient hub airports, by which I mostly mean "not ORD"
(To be fair, once McNamara opened DTW became really nice to connect through; ATL always was designed right, and MSP's only real weak spot for me is the frequent need to cross through the main shopping concourse between F/G and D/E/C.)
- Wifi-equipped F/Y+/Y layout aircraft on almost all routes these days
- Helpful friendly agents (especially in the SC)...and they reopened the A7 BOS SC!
Some negatives:
- Mediocre partners, though the VS partnership has improved this a bunch
- JFK as a hub? Seriously? T4B is too freaking long, T2 is better than it used to be but still second tier at best, and the insane taxi waits.... The T4 SC is nice though.
- SLC as a hub; the "fingers" layout is like the old PM (and pre-McNamara) NW operation in DTW, which I always disliked, but at least it's a small enough airport that it doesn't get in my way too often. SLC really needs a bigger SC and/or more SCs. (OTOH it beats DEN both operationally and because it doesn't have crazypants conspiracy theories about it or an Evil Killer Horse Statue)