For SP I used to use 2 AR's with ACOG/12 X scope (550/M8 or 550/SCAR etc) Mk23. with large mag & Incendiary/ frag grenades. I just made the puppets toss smoke/flashbangs etc.

for MP/TH I used an AR (550/SCAR/M8 etc) and either the SPAS 12 (no attachement) or the AUG SMG with a large mag for emergency/CQB stuff depending on the mission. Pistol is always MK 23. with large mag and then Frags/Incendiary/C4 etc. again depending on the mission

G3KA, M8 and G36C are my picks. G36C is slightly more accurate than the M8, which is slightly more accurate than the G3KA. But the G3KA and M8 do more damage than the G36C. Ultimately I prefer the G3KA with ACOG.