M416 is better for the same reason in the real world people choose the Ak 47, its simple, pick up and use.
The SG550 has a smaller clip and the crossairs open up bigger than a MG if you spray at close range.
I found that the SG had more recoil in scope too.
It takes quite a bit of getting use to compared to the M416.
I agree with Moo, its better all round compared to the SG550