It is very easy to hold BOS out of training. If not during training, you can trade there fairly quickly and easily. From an open time perspective, I'd avoid the 220 until they get more aircraft, as the pot is rather limited at the moment and I believe they're overstaffed due to aircraft delivery delays.
However, it's very easy to earn extra and work premium or broken pairings out of BOS on the 320. Flying is a mix of everything, with the SQ flying increasing as well from BOS (Amsterdam, Paris, London).
Trip trading and swapping can be difficult in the busier months, but generally easy to do once you've figured out FLICA and the how the grid works (although needs a lot of change in the JCBA). Average BOS 4 day trip for a junior lineholder is often an island or Florida turn somewhere on day one with an in-base layover, followed by a west coast transcon and then a redeye back on the last day.
I would never advocate commuting over living in base, especially as the NB rates at Delta are only a few more $ than what you'd earn here (profit sharing aside...).
Good luck with your decision.