Originally Posted by
jon503
Adding on to FPC552's excellent hints, a few more considerations:
OZ miles have a much longer validity than UA miles, so if you're not looking at redeeming them within the next few years (e.g. because you want to wait for more miles to be added from the occasional *A flight), then the OZ program is better than UA.
On the other hand, I've found UA's FFP one of the best ones for actually redeeming miles. Back when I was using their FFP, at least, they only charged a nominal processing fee of 5-15 dollars for a flight, meaning that they were pretty much truly "free" bonus flights, as opposed to OZ, where a flight in Y ends up costing pretty much half the regular fare. Also, if you're US-based, UA offers a lot of alternative ways of using miles, such as magazine subscriptions or their online shopping mall. Haven't found anything of interest in the latter myself, but I picked up a cheap WSJ subscription to use most of my last remaining miles recently.
Well, UA actually allows one to extend the life of the mileage balance with any activity within an 18 month period. Thus, UA miles can potentially have a much longer shelf life with minimal work. One major down side with UA is the upcoming changes on earning miles, especially for regular members, whereas the number of miles earned is based on the cost of the ticket (at least on UA metal, it's unclear how this scheme is applied to partner tickets).
LAX