It depends. They don't get better stats, and only some of the moves are better. In some cases, the Max Move is better (i.e. Max Knuckle is better than G-Max Chi Strike). However, the G-Max move is on occasion better, or can be better. G-Max Resonance is better than Max Hailstorm, setting up Aurora Veil, which is in most cases better than setting up Hail. A potential move that could be better, but isn't always, is G-Max Gold Rush. This is generally better when you want to farm money.
So they don't have better stats, and the moves are only better on occasion.
Hope I helped!