I fly which ever is least expensive. Both Song and Jetblue seem to be equivilent. Both have friendly, efficient flight attendents, onboard TV's, Movies, food. The only difference I see is which terminal they use. OH and Jetblue uses over the head earphones, Song uses earbuds. I just kept the Jetblue ones and use them for each flight, I have used them for over 5 flights.
Jetblue's entry door and seats start right behind the door to the pilots door. Song has a forward and rear parts of the plane. Go with the least expensive for each leg of the trip. I often fly out on one and fly back on the other. You can get better prices doing this frequently. I am flying out on Jetblue for $79 Song wanted $124. and flying return on Song $69 Jetblue wanted $104.
Have a great trip no matter which you choose.