Well, what type of field do you play on?
I love the look and the feel of 552. The gun feels even better than an mp5 and is extremely compact.
The g3 will probably have better range, but it is LONG. It has a much higher mag cap, but weighs more also.
It just depends what your role is and what type of field.
I'd go with the 552, but that's just me.
Also, the 552's mags clamp together like a g36