AFAIK, the differences between the three technologies are as follows: Roland is a synth, which is only triggered by the guitar. That means it doesn't process your tone or, in other words, every guitar sounds equal through the Roland.

On the other hand, the Variax processes the true tone from the guitar and models some well known axes. The output is, however, analog, which I consider a flaw. But, I expect that in the future this feature will be added, as well as digital inputs to modelling amps. IMO Line 6 should also sell this modelling unit without a guitar, because different players like different axes. Some kind of calibration would have to take place then.

The MaGIC system is an attempt to develop a digital transmission system for audio data (low latency!). I've been watching this stuff for a while; Gibson is not the only company developing such networks. A bigger attempt backed by many PA companies is CobraNet,
which is already in use.

That being said, I like the Variax concept and digital transmission, because it reduces hum and noise. The guitar synth stuff seems less useful to me, but that's now and may change.

Just wanted to share my thoughts on that stuff, have a good one! Pete