i would say start off using the famas pre-made class until you reach rank 8, as soon as you reach rank 8 use the SCAR-H assault rifle, its 1 of the most popular on the game and 1 of the few guns which kills in 2 hits(with stopping power), also imo its got the best iron sights in the game so you can use other attachments than sights.
i'd also suggest giving the heartbeat sensor a go(unlocked after 15 kills with a silencer on the gun) its basically a personal uav attached to your gun(short range) its good for your classic camper or for a more cautious run nd gunner.
for perk 1 i'd suggest sleight of hand until you unlock scavenger.
for perk 2, stopping power.
for perk 3, for s&d use ninja(lots of ppl use heart sensors so its good as it stops you appearing on them), or for other game modes use commando or steady aim.
also id recommend using the spas-12 shotgun as your secondary weapon, its got brilliant range for a shotgun.