I like sinister looking weaponary, so I chose the MP5 normally, it just looks mean, sleek and nasty.
I like guns that look like evil things with evil intentions, like the MP5 for instance, I reckon if left to its own devices it would go rob and old lady, all of its own accord. But it doesn't need the money oh no! after all its just a gun, it purely does it to pass the time!
edit, furthermore, I'm a sucker for hard things in games, so I like the fast car that doesn't turn very well, and for guns, the MP5 normally is the worse of the SMG's, doesn't live up to the AK47 but thats what I like, things that are hard to handle.