I find my best class load out in BFBC2 to be the following for squad team deathmatch
Assault class= unlimited ammo
Primary weapon (AA12)
Secondary weapon (M93)
Gadget (C4) for those tanks
Spec 1 (Am UPGR)
Spec 2 (SG UPGR)
Spec 3 (V ALT W)
This setup seems to work best for me when playing squad death match but keep in mind that I usually have a full party or 3 people that all play supporting roles. The support roles of the team members is key to victory. We usually have one running recon kit spotter scope who stays away from action but is key to enemy location. If full party 2 running assualt with etiher shotguns or 1 with assault rifle and last guy running med kit to defib a downed team mate or to drop med kits to heal after a close gun battle.
Feed back as well as criticism is welcomed as I am always looking to become a better player.