Welcome to Flyertalk. You will receive much better answers if you list the program balances that you hold, and the route you hope to fly. There are important exceptions to every generalization. For example, many programs allow one-way redemptions for half the miles of a round trip, this makes it possible to use one airline eastbound and the other for the return. Likewise, most airlines belong to one of three alliances and offer travel on any airline in the same alliance. This means you may be able to redeem for two tickets on the same flight through two separate programs.