I'd do it because it is way more convenient and reliable, plus the lounge issue. I've taken several LGA-BOS shuttle flights this year and each time found the DL option to be incredibly convenient and flexible - way more than CO. The concept of walking in to the airport, picking up a snack and then walking on to the plane, regardless of the ticketed flight time is something that makes the Shuttle truly wonderful. Add on free beer/wine and 34" pitch on the plane and it is hard to go wrong. Plus, the flights are a cash cow for DL so DL seems to give them priority for ATC when the weather turns. CO has to focus on their transcons and TATL flights, leaving the BOS (and CHI) flights subject to serious delays and cancellations. And I've never really had enough time in BOS to need to bother with the lounge because of the whole walk in and get on a plane concept. Oh, and the Marine Air Terminal kicks EWR's butt any day of the week.

Plus, full credit on my CO account. What's not to love?