Golden AK47 FTW.
Its one-shot kill on any man, juggernaut or not. Don't need a red dot sight, it makes the recoil more.
M4 Carbine double tap FTW.
Very accurate, kills with 2-3 shots, juggernaut or not. Red dot is recommended, but silencer is okay.
AK-74u FTW.
Don't put any attachments like the AK47. Kills with 1 shot close range, 2-3 shot anywhere else. I put extreme conditioning because thers no need for steady aim, but dead silence is good too.
Not much of a fan of LMG's, but if i were to chose, it would be RPD with grip. Pretty strong, IMO shoots more accurately from the hip than SAW.
SNIPER?
Go with the M40 or barret, definately.
both are 1 shot kills, unless jugg, or shot to the knee.