Alright...here's my take on things:
GSG-5: $500.00 copy of a (let's say) $2,000.00 MP5
AK: $500.00 copy of a...$500.00...AK-47
The GSG-5 is cool because it allows people to own a VERY GOOD copy of a gun that's legally and financially un-attainable for most shooters. The AK doesn't offer that same appeal; it's cool if you want to save on ammo, but for the same money, one could buy an actual AK-47.
Another thing about the GSG is that the "silencer" fools people even more-so. They see you with an MP-5, and even though it sounds like a .22, they wonder if it is, or a real-deal silenced MP5.
For me personally, I'd buy the Sig Sauer (522) .22lr before the GSG any day of the week.