I use only the Hilton and Starwood programs. I spend a lot of time on business travel at mid-range hotels which sometimes limits my Starwood stays. Hilton has a good range of hotels throughout every price range and they're in a lot more locations than Starwood. They also have some good high-end hotels (mostly international though) to spend points on. The other good thing about Hilton is that your points (and free nights due to recent promos) build up very quickly and if you're a diamond member, you can usually get a reward reservation pretty easily.

I like the Starwood properties a lot and it's easy to redeem points, but the points build up a lot more slowly than the Hilton points. Additionally, I almost never get targeted for Starwood promotions. That also limits my stays there.