As you get information on this subject, remember that free flight the quickest is not the only factor to answer your question. Delta airline FF program is referred to often on this board as skypesos, because you can accumulate a lot of miles, but never find flights to use them on. United is pushing their program as "wanting you to use your miles." This implies that they are friendly to using miles, and I would probably agree with United having a good program. Also look at what airlines service the cities you would use the flights for- important if you have a free flight, but it doesn't go where you want. Hope this helps a little