The only CoD game I ever played extensively was the first Black Ops, mainly because it just had the best loadout system and overall gameplay "feel" of all the CoD games I had tried. I was always terrible at maintaining a decent K/D ratio, as I hated camping and much preferred just running around, though I was somewhat decent at scenarios like CTF and Headquarters.
My preferred loadout involved using the Skorpion with a grip as my main weapon, as it had great accuracy and dealt a lot of damage at short range, a Strela 3 rocket launcher as my secondary so that I could take down enemy spy planes, concussion grenades to slow other players down, semtex grenades just because I'm a fan of "sticky" grenades in FPSs, claymores for area denial, and for my perks I used marathon, lightweight, and sleight of hand.
To be truthful however, i think a big part of the reason why I focused so much on a speed-based build was just to compensate for my terrible reflexes. I've read that aspies typically have slower reflexes and reaction times than NTs, and judging by the number of times I've been sniped by people in various FPSs just as I was about to pull the trigger on my own weapon, this doesn't surprise me.