i feel like the mp5 is a cross between a smg and machine pistol. the one reason that people choose it is because of its damage and fire rate. im all about range and as a primary, its range doesnt cut it for me. even when reducing its recoil with a silencer, its range is terrible.
The P90 with a silencer is overall better then the MP5k with a silencer. Each have advantages though. MP5k is more viable w/o stopping power. P90 has a larger clip.
I personally like the MP5K more. I used to like the P90, and I still do, but I like the MP5K more. Plus it just wrecks in Search and Destroy with a silencer.
Vector also has the smallest clip size and the least amount of damage. so you cant really use lightweight with it. MP5k works fine for me but i use it on the smaller more crowded maps because of the range issue. The p90 can do terrible things for your accuracy though. it fires so many bullets so fast that if you miss your accuracy plumits. Its kinda like having a miny lmg with greater mobility since the clip size is so large which is a plus. However, the fire rate keeps it from feeling like it has that large of a clip.