Here's a tip for people who use shotguns. I will actually go through all of the shotguns and go through each of them and show you which ones to use too.
USAS is an automatic shotgun, so you can just hold down the shoot button. It's easy to take out multiple enemies up close. There's 9 bullets and the damage is 25, 5. That's 225 damage upclose, 45 damage mid and far. Good iron sights. Low Ammo. Need Extra mags. Shoots at 139 rounds per minute.
KSG is a pump action shotgun. It fires at 60 rounds per minute. The bullets do 28, 15. Each pellet holds 9 bullets. That's 252 up close, far away 135. Good for 1v1 close combat. Bad for fighting more than 1v1. Semi good range. Bad iron sights.
Spas is a pump action shotgun. Fires at 60 rounds per minute. The bullets do 30 damage each up close, 14 far away. 8 bullets in each pellet. That's 240 damage up close, 112 far away. Good iron sights. Good for 1v1 close combat. Bad for fighting more than 1v1. Good range.
AA12 is an automatic shotgun. Heavily nerfed. Low ammo. 15 damage up close, 5 far away. 8 bullets in each pellet. That's 120 up close, 40 far away. Good for taking out multiple enemies. Fires at 689 rounds per minute. Terrible range.
Striker is a semi automatic shotgun. It fires at 352 rounds per minute. It has 6 bullets in each pellet. It does 25 damage per bullet up close, 15 far away. That's 150 upclose, 90 far away. Good with extra mags. Terrible iron sights. Semi good range. Good for 1v1 and multiple enemies.
1887 is a lever shotgun. It fires at 60 rounds per minute. Pellets hold 8 bullets. Each bullet does 30 damage up close, 20 far. That's 240 up close, 160 far away. It has 5 shells in each magazine. No attachments. Good range. Good iron sights. Good for 1v1 combat.
Now I'm going to tell you what I think is the best shotguns at of all of them. Next I will give you tips on how to use them.
How to use AA12. Don't use AA12 until you unlock scavenger. Turn on specialist strike package and use sleight of hand pro as your first killstreak. The perks you want is Scavenger, hardline, steady aim. Try to have them all pro. What happens when you don't have scavenger and no specialist wth sleight is that you will lose all your ammo on your first 2 guys and you can't pick up any ammo. Once you get a kill you will be out of ammo so you have to reload. Takes a while without sleight. Once you get your weapon to level 28, that's when the good part comes in. Put on damage and extra mags and you'll be able to take care of all the team. You should take each of them in 2 bullets. Remember it has terrible range.
KSG is plain and simple. Get your weapon to level 28 and use damage and grip. You want accurate shots instead of more ammo. Why? Because you're not going to use all the 8 shells in the magazine. I doub't you'll ever use 4 without reloading. You have enough ammo without extra mags. Just try to keep your hipfires as accurate as possible so you can kill them in 1 hit.
SPAS is the same as KSG except get extra mags instead of grip.
Tip 1: Don't ADS! Do NOT ADS! Only ADS when they're literally 20-40 yards away. They shoot the bullets out, not in. You have a more accurate shot with Grip + Steady Aim, than Grip + Steady Aim + ADS.
Tip 2: Ride at a 2-4 sensitivity. Do not ride at a 8-9. This isn't trick shotting. All you need is to see the person and blast him.
Tip 3: Do not go into battlezones with pump actions. Use AA12 or Striker for the battlezones. A battlezone is the most populated area of the map. Where all the kills mostly take place. Ex: Hardhat... You know where everyone is at.
Tip 4: Use concussion gernades. Don't stun yourself with a flash gernade. Use a quick concussion as you don't need to not look at it when throwing it. It also stuns them so you won't get Akimbo'd by FMG9 when they're flashed.