I fly both of them, but prefer JB. I used to love Delta Song, and when that went away, I moved over to JB. I prefer the televisions on JB..it tends to make the time go by faster. I like the personel on JB better also. Delta can be booked much further out, but they make many changes before departure day comes. You really have to stay on top of them and their myriad changes. JB doesn't book nearly as early as Delta, but they don't make many changes once they put their flights up. And, when they do make a change, I have always known about it well in advance of my flight. Delta waits until the very last minute to notify the passenger of any changes. Of course, that could be because they make so many changes..they would be sending me emails every month!!
Where to fly out of depends on how much you want to spend and how much your time is worth to you. We are pretty equidistant between Logan, Manchester NH, and TF Green. Logan is about 40 mins away, Green is almost exactly an hour, as is Manchester. If I fly SW, I head to Green. JB and Delta I fly out of Logan. It all depends on cost and time of day of flights.