I have ridden both forms in the last couple years along the east coast. I prefer vario grip over Magne-Traction. I did find Magne-Traction a bit to sticky for me, even though it did dig in very well in the ice, Vario Grip was much smoother for transitioning from edge to edge for me while still having great bite. Once either one is locked into a turn the perform the same task,
Edge hold will be fine with either system for the most part. Just boils down to you as a rider though, skill level and riding style plays more of a role in ice then the edge tech in my opinion. For me the main issue is the I do not have to work the board as much with Vario as I do with Magne(talking about the stickiness of transitions that I experience)which equates to less fatigue.