Mp40.

Next.

MW - AK-47 / M40A3

WAW - MP40 / Kar98K

MW2 - ACR / AK-47 / Intervention

Black ops(worst game) Famas...(for the short time i played it)

MW3 - ACR / MSR

I love ARs and Snipers xD

cod4 - g36c

waw - stg 44

mw2 - tar 21

black ops - ak-47

mw3 - acr

M4A1, its always been consistent. 

I guess my overall favorite however would be the TAR21 from MW2. 

I played the demo for COD 2, and by far the best is the BEN LMG, one of the first LMGs you could get, faster reloaded speed then many of MW3's Shotguns (without slight of hand), yet its mobility was not as good as Subs but better then most snipers and nearly as good as Ausults, plus it was an added bonus of 100 bullets per mag and you carried 5 full mags in COD 2, best gun by far, only problem was the iron sights (you could only see 10 meters in front of you), but putting Red Dot Fixes that and the range is amazing

ACR from mw2. Definition of Laser beam

CoD4: M16
MW2: FAMAS, ACR
BO: FAMAS
MW3: ACR

Overall winner: 925 RPM burst fire weapons in the games with stopping power
(M16 in CoD4, FAMAS and M16 in MW2)

Think type 95 with considerably longer 2 hit kill range while the weapon always kills in 2-3 hits.

MP7 with MP9 akimbo as secondary and i do like the ACR and AS50

COD 4's M16...oh how I miss that M16

M93 Raffica. It's like having an M16 in your back pocket, lol. It was absolutely broken in Hardcore. I would take that hands down over every other gun in MW2. While people were raging(and rightly so) over akimbo 1887's I was headshotting people across the map with the Raffica and laughing my ass off the whole time.