I’m not experienced, and quite frankly terrible, with the assault class. But I’ve been thinking about mixing it up lately to make my gaming experience better, so what are your recommendations? I mainly struggle feeling comfortable with an assault gun so recommendations on the best options would be awesome. Usually play on hardcore servers, if that impacts choices. 
What guns do you usually use?
Depends. When I’m recon, I usually use the Gol-Magnum and switch sites depending on map. I usually play Operation Metro, so usually have a medium scope on it. When in Support I boss the MG4 pretty much all the time. For engineer I’m usually a shotgunner. So as you probably have noticed I stick away from AR & Carbines so don’t have much knowledge of any of them. EG, is it worth sacrificing rate of fire on AR if there s a gun with better all round stats? Or should rate of fire be the most important stat?
I think rate of fire can be important but many times it comes down to preference. I would play around with a couple different weapons to see how they feel.
I find the AN-94 an excellent Assault choice and easy to get used to .. Very accurate .
For a carbine, I’m currently using the A-91 with red dot, stubby/potato, and suppressor. Great in CQC, and pretty nice at mid range as long as you burst your fire. You don’t see many people use it also, so it’s semi unique.
The main popular carbines are AEK, SG553, and something else I’m forgetting currently.