They are almost all the worst (or the best*, if you are a glass half full person). As noted up-thread, it all depends, which is why it is so important to diversify. Just had a call from a son: he just got a much-desired interview 3 days from now in Chicago, lives by a small airport with limited flights, can't leave school until Thursday and has to be back before Monday. The cheapest ticket is almost $800 rt. Luckily, I've been trying to build up my stash of United miles; just as luckily, I have AA miles. One way, and only one way, was available on one of them for 12,500, and the other way (and only that way) was available on the other for 12,500. I'm happy, but if I didn't have miles in multiple plans, I would have had to spend more miles.

*There are, of course, exceptions to the sweeping generalization. For instance, I find it really tough to work with USAirways because they don't allow one-way awards.