Well I've been using CM Nightlies since they came out and I can't go back
CM is faster, you have ART, the sound mixer is allot better, tones of CM themes on the play store... etc...
With stock Sony Rom you have noise cancellation but the sound with those headphones and equalizer is bad I have to say. The X-reality is quite nice but unfortunately only works with the Sony App Album witch I personal don't like.
The only thing that I miss is the camera that in the Stock Sony Rom is better... but for the rest CM rules big time!