Initially I played CoD4 on the 360, but I have since migrated to the PC version (new GPU arriving tomorrow so I can finally play it with all the bells and whistles cranked to "awesome"). It's a bit amusing to see the different preferred weapons between the platforms. On the consoles, the M16 & P90 are generally the most common weapons (aside from your standard red-dot MP5) but on the PC side, the AK-47 is far and away the favorite assault rifle. Because there's no aim-assist, you're almost gimping yourself by using the M-16 due to it's burst-fire.
Many more players on the PC side have also appeared to have realized that the AK-74U is one motherfucker of an SMG with no attachments. After almost every game someone makes some snarky comment in the chat towards anyone who used the "overpowered AK-74U".
Although I wouldn't necessarily consider the PC version to be superior, partially due to the map size-player ratios. It's clear that CoD4's maps were designed with the player cap on consoles in mind. On the PC-side, where you can have dozens of players on each map, it's just a cluster-fuck of grenades and martyrdoms, particularly on the smaller maps; amplified by the fact that you can have 20-something players per-team.
Although I never join games that large, and really don't see how anyone could and enjoy it.