It depends entirely on what level I am at the time of making the class, but if you want my level 70 favorite class, here it is:
Primary Weapon: AK-47 with Extended Magazines or FMJ
Secondary Weapon: AT-4 or RPG-7's
Equipment: C4 or Claymore
Special Grenade: Flashbang
Perk One: Marathon Pro
Perk Two: Lightweight Pro or Cold Blooded Pro
Perk Three: Ninja Pro
The AK-47 is my favorite gun in the game, hands down. It does appear to have a lot of recoil, but intentionally or not, the recoil is timed to reset the level of the gun between shots so your bullets still go where you originally aimed. It has a crapload of power, and I just like the gun in general including looks. I obviously can't start out with FMJ, so I use Red Dot Sight until I unlock FMJ, then I use FMJ until I unlock extended magazines. You may think Extended Magazines are kind of noobish, and while I agree to the extent in a spray-and-pray situation, I take careful aim with my shots and rarely find myself going full auto for more than a few seconds, I just like the peace of mind of knowing I don't have to reload as frequently if I get in a tight spot.
The AT-4 and RPG-7 have pro's and cons that lead to me switching off between them. The AT-4 is damned accurate, I can put it through windows across the map, but you only get one, and I've found it has less damage though I don't know if that's true or not. The RPG-7 comes with 2 rockets, allowing an extra use, but are a lot less accurate. It depends on how big the maps are which one I use.
Using flashbang allows me to not only clear rooms more effectively, but is very useful for situations where I need to get through a claymore without setting it off and alerting the enemy to my presence. Now the flashbang does make some noise but hopefully I can get away before he notices, and by doing this I don't have to worry about getting caught on obstacles and taking damage from the claymore.
I like C4 because it allows me to set traps and has a bigger blast radius than claymores do, and has a 360 degree blast, but you do have to be alive to trigger it. I use sound to know when to set it off, so I don't have to actually watch the doorway or wherever I throw it. Claymores allow me to do one of two things. I can use it as an advanced warning system to find out where someone is, or I can use it to block access to a certain area, both have ups and downs.
I don't use Marathon Pro for the ability to run forever, I use it for the increased hurdle speed. I honestly couldn't care less how long I can sprint as I don't usually find myself trying to cross the entire map at once, but the ability to climb up/over objects has saved my life more times than I can count. Lightweight is pretty much a necessity in my playing style in my opinion. I pick a location, stop for 1-2 kills, sprint to somewhere else, rinse, and repeat. Lightweight allows me to minimize the time between switching locations which reduces my chance of dying. The pro of it is helpful if I get caught sprinting, but I rarely have to make use of it. I do have a copy of this class with Cold Blooded Pro on it for instances where I find the need to be sneaky, or if the opposing team gets one of the higher kill streaks so I can run around without worrying about it. Now for ninja pro. For me this perk is make or break, I don't want some camper with a heartbeat monitor finding me, but the pro is even more useful...I can sneak up on people undetected even while sprinting, I can climb up ladders noiselessly, and it allows me to hear enemies footsteps more easily since I don't have the noise from mine getting in the way.
I do use painkiller which I sometimes catch flak for, but copycat is essentially useless for me, and I am morally opposed to martyrdom like I was in Call of Duty 4. Final Stand can be good, but the few times I've tried it out and actually managed to get a 4 death streak (not easy for me at all....I don't let myself get spawn trapped), it didn't turn out to help. Painkiller has helped me whenever I end up activating it, and when I don't it doesn't matter.
Anyway, this is my class of choice, of course, since I prestige after a few hours of being 70 I rarely have this class for long....thank god I'm 9th prestige now so soon I'll be able to use it exclusively.
I just made a new class today, which is now my favorite ever:
Cold Blooded Pro
I used to use a very similar class, but with a silenced scar, but this class is ridiculous amounts better. The tar has a higher rate of fire, a larger clip, a higher starting ammo count, and the same damage as the scar.
I've only started using this class today, but I can forsee this becoming my favorite, and most used class in no time. I can't believe I never thought of silencing the tar until today.