assault:
M16A4 - laser sight
M14 - laser sight
sub:
AK-74u - silencer
light machine:
RPD - grip
shotgun:
M1014 - laser sight
sniper:
M40A3 - nothing
both assaultguns are weapons that require skill in order to be effective, the M16A4 gives a 3 bullet burst and is fatal if 2 of the 3 bullets hit in the chest but it's bad side is that it is hard to use in close encounters.
the M14 is one of the few weapons that can kill enemies with a single round if aimed high on the chest and on the head, it's a semi shooter and perfect for mid and long range, however watch out with close encounters, hits with this weapon may be very effective but it's hard to defend attacks from close unless prepared.
the AK-74u silenced is also very effective on short range and is very useful in search and destroy, 2-3 hits kill with this gun, it has plenty of rounds to go around with.
the RPD with grip is effective at long range if done right and is already fatal with merely 2 hits. the grip makes it very accurate, but do know that the reloading takes long so only do that in save conditions.
the shotgun is the strongest weapon but it can never be effectively used past 10 meters so use it in small maps only, using the aim is not needed but do make sure that you have a clear shot which is fatal in one shot or the opponent retaliates.
the M40A3 is my favorite, it's accurate, strong, plenty of rounds, and gives low recoil, it's the best weapon among the snipers because the others lack of bullets, high recoil, or power. besides that it's easy to reload it after every kill. the chanse is high that it kills in one shot and if not it is ready to shoot again in no-time.
all these weapons are combined with the perks i mentioned earlier, it's not allways easy to use them but i think you will like it