Still going back and forth between Red Dot and Grip on the M60.
I tried using the other weapons like the M16 and P90 but I just love the M60's power.
I think it depends on which map I'm playing as to whether I like the Red Dot or Grip.
I also really like how balanced the game is. Grip = no perk 1. Grenade launcher = no perk 1. Go for red dot, no grenade launcher. For every perk or item attachment you give up something to gain something so it's all very personalized. My favorite multiplayer map is still Overgrown.
Hardcore servers are pretty fun too. I find it odd that I still own face on hardcore servers even though the M60 is much less accurate than any of the other hardcore-usual weapons. I think playstyle, anticipation, and being able to react immediately to any screwy situations is a huge factor in COD4.