C7A2 has the collapsable stock, but after seeing a few real ones and a couple of airsoft replicas, I can say I don't care much for the look at all. I tend to prefer function over cosmetics, so I went for the C7A1 look and kept the full stock. I couldn't imaging giving up my large 9.6V 3800 mAh battery...
And besides, I tend to prefer the full stock anyway. It's not like we're getting in and out of cramped armours vehicles or having to adjust the stock for 4" thick body armour in airsoft. The advantages of the collapsible stock over the full stock are far more minimal than they are in the world of real steel.