User blog comment:Callofduty4/Favorite SMG in MW2?/@comment-958222-20100207075220

The MP5K or the UMP. Both kickass at all ranges due to high power (UMP) and good RoF combined with awesome iron sights (MP5K).

And to anonymous user, SMGs have small penetration because SMGs fire pistol rounds, and are not usually designed for penetrating surfaces (the P90 is one exemption I know of, but balance dictates they should all be the same)