I have the following setup:
Primary: K-VOLT (No attachments unlocked yet, jsut started using it)
Secondary: AY69 w/Extended mags (Next comes the silencer)
Explosive: Frag Grenade
Armour Module: Armour Enhance III
Stealth Module: Stealth Enhance II (Just about have level III unlocked)
Power Module: Weapon Pro II (Just started using this, but it's a fast unlock)
For a while I was using Point fire enhance, just till I unlocked it to level III, but now I am going to unlock Weapon Pro to level III and then after that I will switch to Mobility Enhance and unlock all those levels.
I think once I have Mobility Enhance unlocked I will basically use that all the time.
The only thing I seem to ever change in my classes is the primary weapon. Right now the K-Volt is my main, but I'm not sure how much I like it. I was using the Feline but it didn't seem to be dropping guys, so if I decide to drop the K-Volt I will probably just switch back to the SCAR.