We mostly use our FF miles on AA and BA and airlines in the One World Alliance. We have always been able to use our 2 for 1 BA tickets but it is NOT easy. We got four of us to South Africa in July this year on those tickets (family safari).

We have Delta miles but the awards levels are so much higher not sure when we will ever use them.

AA has always been the easiest to redeem (unless we are tying to get Qantas that airline has become almost impossible) I also find AA's website the best but of course that is because I am so used to using it.