As a PC Call of Duty 4 veteran, I have ran a number of different and exciting custom classes throughout my playing career. I will list 2 of my favourites with explanations of playstyle and why I chose them. Each I described will be very unique, one is a run-and-gun class and one a class for explosive fun. The second class will be discussed in a seperate blogpost.
My first custom classes, the "Run-N-Gun", consists of the P90 Silenced as the primary, Desert Eagle as secondary, Bandolier, Stopping Power and finally Steady, with Stun Grenade as the special grenade. I choose the P90 as it has a large clip which allows for continued action without reloading, and as it very well with Steady Aim, giving your a very small crosshair, and allows for running and gunning without needing to aim down the sights. Also, a glitch that is not very commonly known allows the holder of the P90 to strangely run further than other SMG's, akin to running Extreme Conditioning without really running the perk.
I choose the Desert Eagle as my secondary as it is very powerful and can easily 2-hit enemies as close range of 3-hit enemies at further range, and be quickly bursted with a quick finger. Bandolier fits well with my cautious assasin playstyle, as I often stay alive for a long time and often spray to provide covering fire. Stopping Power is very powerful and allows the P90 and Desert Eagle to excel at close range, killing enemies before they usually have a time to react. As discussed previously, the P90 meshes nicely with the P90, allowing for accurate spraying at short to mid range. I run the stun as my special grenade as it better than the flash and smoke grenade in almost all circumstances.