Probably the keyboard version. The G2 rack lacks all kind of goodies like knobs and the 4 inputs found on the keys. You can also attach a microphone directly to the keyboard, not possible on the G2 Engine.
Oh goody I'm looking forward to this. The G2 sound examples really are mindblowing. Hopefully there'll be more synth examples soon. This is an analog modeller and it sounds like a VL-7.
Analog modeling, FM, and Physical Modelling. The demos feature acoustic and electric guitars using a "plucked string" physical model, I think. Plus all sorts of MIDI processing. All this in about 12 lbs, I estimate.