Best weapon in MW2 for multiplayer.?

I personally like using my UMP with holographic or silencer or heart beat sensor. Me and some friends think that the UMP is the best but I like the M4. I'm a hardcore type of player so I don't need stopping power unless I'm playing regular TDM. I also like everyone love the Intervention, in hardcore I use the heart beat sensor along with Cold-Blooded and Steady Aim or Commando (both Pro). But I want to know other's opinions on the weapons.