I will repeat what I have written on the DL forum in the past. I have flown DL for 30+ years. They have been as professional as they come. RA has Delta running on all 8 cylinders. Next week the numbers come out. Everything points to DL being on top again.
Now if redeeming your miles is the overriding concern, most people will tell you DL is not the best at this, but to be honest UA and AA are probably heading in the same direction. If you just want to know you can have a professional experience on your trip, and return home hopefully on time, DL is a no-brainer.
NOW with that said, and as I have said before, the other airline I fly at times is US. Never had a problem with them. Are they as polished as DL...no...but they have always done a good job.
YMMV...and I don't know how picky you are about things, but I think you will be happy with DL.