hi-speed USB
its ace, took a while to get used to, because it works slightly differently to other controllers.
Its uses a software server, which acts as an intermediary between the controller and whatever needs to be controlled. Which is a bit confusing at first, but then quickly becomes amazing because you can have loads of different midi maps saved on top of each other. So one map controls your DAW, another map your FX, another map a softare instruments and you can quickly flick through the maps to control whatever you want.
Plus pretty much every plugin ever comes pre-mapped - so you can just choose what pot or slider controls what function using a nice visual display, instead of having to map CC numbers, of twiddle every knob you want to control every controller.
Big thumbs up so far.