I have a couple trips coming up and I would like to use miles for one of them to cut down on cost. I have just shy of 90,000 DL miles and about 85,000 AA miles. Both accounts have more miles pending so they will both grow. One of the two I want to save and use on a miles upgrade to business class TATL in October. In your past experiance is it easier on DL or AA to buy a ticket and then upgrade using miles? Whichever airline is the consensus for being easier to do this I will use the other airlines miles for the two r/t domestic tickets I need. Thank you for your advice.