Ok in my opinion:
Sniper - L115A3 for sure, 1hko, and the scope zooms in about as much as a 50 cal 2nd zoom with high accuracy. This is better than the 50cal because you cna still quickscope, and it is much more accurate than an arctic giving it a huge advantage in ranged combat.
Alt: M24A3, it 1hkos 80% anyways with 100% accuracy and higher portability and faster fire rate
AR - M416 CQB, a very good mid range weapon with near no recoil, I assume this is what you want since you're also getting a SMG. It also 4 hits normally. with a decent fire rate.
If you want close ranged go for REC7 or something of the AK series. The reason no G36 is 1) it's GP, 2) It's recoil makes it require tapfiring when scoped in, the scope has too much zoom for mid range. SO it's good at close or long range.
SMG- UMP45, no competition, a 3hko SMG is just too beast. A MP7 is OK I guess but it does a lot less damage with a lot higher fire rate = pretty much a better spray weapon but if you can kind of aim the UMP is better.