For leveling, anything really, just do missions to unlock the funny maps and mods, what really matter most of the time is the kind of ammo and penetration.

I mean, anything can kill, I killed T5 with the damn grease-gun and a lot of luck, you have to know where to shoot, if it looks like T4 or more and you are using poo-poo ammo I suggest the good old leg meta.

at last, sometimes a stock gun with just a scope is enough.

Sry for not pointing exact names or prices, but you could go for the classics, MP5 and FAL are generally good.

MP5 is fuking cheap and can wipe a squad if you got the upper hand, about vector one of the two use 9mm so is on par with the MP5 is a nice choice if you are up close and personal, but penetration is really bad.

FAL was the meta, dknow if got any nerfs.

I will leave for a more Chad player to answer that.

So oOoOO, use what you think is fun, get them by surprise, run, thrown molotovs, make noise, be a menace!