Bullet Wise....
The 5.56mm and the 9mm cannot be compared, one is a rifle round the a pistol. The 9mm has about 1/3 less muzzle energy than a 5.56mm, there is no comparison and depends on the situation and mission. I like the MP5 for urban situations involved clearing buildings, while I prefer the M16 for standard infantry operations. The best compromise is the M4, but in a urban situation, the penetration of the 5.56 may be a problem in a building.