I ran the Spektrum Pro setup with my M8 last season and part of this season. I just switched to the Airtronics DSSS system, and I can't honestly tell much of a difference, except that the first few runs with the Airtronics system I was hitting the inside boards of most of the corners. Maybe the Airtronics has a quicker response and it threw my timing off? On the other hand, it was a new track layout that day which I hadn't practiced on, so maybe I just needed to learn the layout...
Honestly, I can't say I can feel a difference between the two... both have worked great for me with no problems.