OMG, guns/weapons talk makes my eyes cross, lol.  :goodjob: 
Based on other FPS games that I play a lot for fun (but not a great player), I tend to use SMG's and Assault Rifles. 
I can't remember other guns because I don't memorize the names of them.
 I just pick up guns off of dead bodies, try them out, and if I like them, I just keep them until they run out of bullets, lol.
If you see me play a CoD game, you will see something like this.....
NPC: You (player)! Use your sniper to snipe those two guys on the roof!
Me: Okay, sir! ......  :goodjob: 
                        .....
                         What's a sniper gun look like, anyway? *switches between many guns and spends many minutes looking for it, only to find out I have dropped it at the beginning of the stage* 
                 Gosh, finally found it! Yay!  
                         ......
                         ..... 
                            :unsure:  Er, how do I use the scope and zoom in, lol?  *experiments with gun for a bit* Oh. 
                           ....
                             .... Now, where are the guys I'm supposed to snipe? *looks at guys* There they are!  :shifty:  *tries to snipe, but misses and enemies are alerted!*  :blush2: 
                              Darn!  :gun:  Just RUN RUN RUN!  *runs shooting like crazy and then gets killed*  :teehee: