The Tech Report has an article comparing various hardware accelerated video encoding solutions. They compare several programs, and test Quicksync and gpu based encoding, as well as basic cpu encoding.
As usual, X264 wins in quality of output.
The X264 programmers are adding OpenCL acceleration for look-ahead within their encoding, and while it is only a small part of the encoding process, this should speed up encoding times considerably, depending on what hardware you are using. The Tech Report got their hands on a beta version of Handbrake using this new OpenCL acceleration.
The OpenCL results were really quite good, as far as picture quality, so this looks like an excellent step forward for X264.
Link is here: http://techreport.com/articles.x/23324