Based in DTW and fly both quite a bit. While DL's in-flight experience is good, I find B6's in-flight experience just a notch higher. Unless I can fly non-stop or the routing is significantly better on DL, I select B6. I've had B6 connections through BOS during all seasons (including Winter) and all have gone well. Even when I have experienced IRROPS with B6, B6 has handled it well.