I use CFEngine -- because of its maturity, wide range of supported platforms, and the amazing support I experienced from the author and community.

I wrote this 3 years ago and it's still true today: http://verticalsysadmin.com/blog/cfengine-is-awesome/

Offering training and consulting on CFEngine has allowed me the privilege of training top-notch talent from all over the world (and to see more of the States).