Audirvana+ here, integrated with iTunes. This means one can basically use the iTunes interface with A+ running the show behind the scenes. It gets even better in a 'headless' setup, I use Apple's 'Remote' app on an iPod touch to control iTunes (and therefore A+).
I have also used Decibel (and before it's release, AyreWave), BitPerfect, Amarra (Trial), iTunes. They all sound good but I am convinced A+ has the edge sonically,especially in the midrange, and it is the most integrated solution for sure.