You cant go wrong with a G36!!! I have never used a Classic army model. However, I have heard good things about the Classic army model with it having 7mm brushings, and a heavyer body. The only negative thing about it is, that the mags have weeker springs. so its best to purchase Marui mags insted. Also you will have to search for mag pouches that will fit your mags. But, the mags can lock together so that is an temporary option.
I have a marui and I love it. You just cant go wrong with a gun that has a V3 gear box. Trust me it will be one of the best purchases you have ever made. If your going to be doing power upgrades in the future, you may want to get a Large hand guard. This way you can house a larger battery like an 8.4 large 1800mAh or even larger. Some people do it differently, but thats what I did to mine. In the future I am going to add a K-.R.A.S Kit.