Almost saved up another 1000 certs, and I need suggestions on what to buy. I've spent 0 SC thoughout my entire game duration, so every single gun I've bought with certs. I've already got the ac-x11, gauss compact s, sweeper and mauler for my light assault. What should I be getting next?
GD-7F, no doubt about it. You already have a godlike long range weapon with the AC-X11 and sweeper/mauler for very close range. GD-7F is a CQC beast, but if you get used to his recoil you'll shred everything at 20-30m Personally i use it with Forward Grip, because i suck controling recoils and i'm taking down people at 30m with ease. Not to say that it still is a beast even without ALS. It's a very versatile weapon. But why to say it, when you can see it (all credit to Iridar51)
If you're looking to improve as a player than you got to keep trying out new playstyles. You seem to be well covered in shotguns and carbines, so I suggest getting an SMG next. Both NC SMGs are very strong, but to a less experienced player I'd recommend the Blitz. GD-7F is a very strong carbine, and it plays different to other NC carbines, so you may go with that as well, though it's more skill demanding than said Blitz or other carbines you've used before.
If you are planning on getting the GD-7F you may want to read about it and learn it's pros and cons, what it can and can't do: https://forums.station.sony.com/ps2/index.php?threads/the-gd-7f.199714/ I do recommend this weapon though, highly recommend
