With AA I normally book one way tickets, there is normally no price difference, you get greater flexibility, can book if you see the perfect outbound at a good price and deal with the return later on, with other airlines you are at a disadvantage booking two one ways, but it has allowed me to book the outbound I want, a return that is ok, then if I find a better return I can make the change no jeopardy to the outbound, I have enough miles that I always make sure to book my new flight before cancelling the old flight, but in the end check what you what to book to make sure there is no price difference