For me it's:

NATO:
>AR: SCAR-L Mk2, SA80
>Carbine: M4A1, MCX-SPEAR, SG 553, SCAR-SC
>SMG: MPX, Vector, P90
>LMG: Minimi Mk3, M60, M240, SIG LMG 6.8
>DMR: M1A
>Sniper: M2010, Barrett
>Shotgun: Mossberg 590A1, Benelli M4
>Sidearm: P320, M1911, Five Seven
PAX:
>AR: Kord 6P67, Galil, Tavor 7
>Carbine: AK-205, Grot, QBZ-192
>SMG:
>LMG: RPK
>DMR: SVCh-8.6, SVDM
>Sniper: SV-98M
>Shotgun: KS-K
>Sidearm:

Anything not mentioned is interchangeable between both sides