Basing it on my own experience only, I like AA.

I find they are easiest to redeem and also, you can HOLD award bookings online for a while, whereas most other web sites are far more limiting. AA also HAS seats most of the time for my needs!

I know CO recently has become a better place... I have heard this from many people and that's great. But AA, other than the fact its in flight coffee can be horrid, has at least been consistent for my needs.

Dont forget the credit cards... AA has Citi MC and it gives you 20k for signing up and also, you can catch that 10k or 20k citibanking promo in here too. I have had good experiences with Citibank.

Good luck!
MM