I agree with Ustwo -- hardcore servers seem funner than regular servers. I like them more because they're much more lenient on which gun you use. I see people using the SMGs all the time (normally I never see people using them except the P90).
Recently while playing I was wondering why I kept sucking with the M60. It was all over the place and I couldn't figure out which perk combination yielded the best K : D ratio for me. I was about to start using the P90 or M16 because I kept getting owned so bad.
Then I remembered that I had formatted recently and reinstalled. What do you know, I hadn't installed ANY of the COD4 patches. Reinstalled up to 1.5 and you guessed it: M60 accuracy much, much better. They never went out and officially said that the patches fixed the accuracy but man what a difference. Back to the LMGs for me!!
I've also started to go for the gold M60. All the way done with the M60 challenges and just have the phase 3 headshot challenges to finish for the RPD and M249.
There's nothing quite like sniping someone from halfway across the map with the M60 on hardcore mode. It's campers delight on a lot of maps and it's so satisfying to shoot a single round at someone for the instagib M60 with stopping power.