As a previous UA 1K and now a 1MM, I have not totally given up on UA for DL,but when all else is equal, I choose to fly DL.

I have plenty of UA miles, little time to use them and prefer the experiences at DL . Flights have been on time,planes clean and customer facing employees are generally more pleasant.

I have no experience in trying to redeem Skymiles,which according to FT wisdom,will be difficult if not impossible. But at least for now, my travel experience comes first.