This guide is to help the community and cure my boredom. Please forgive the numerous gramatical errors. All comments are wealcom.
The shotgun is an interesting weapon. It has amazing damage per second and more utility than you might think. Its best used against opponents that don't know you are there yet or have little in the way of cover/mobility options. It tends to have trouble striking evasive foes at close range. This may seem counter intuitive but take a few shots at a dodgy foe and you will see what I mean. Despite this the weapons impressive damage output is reason enough to consider its usage.
1. Deffault - fire rounds: Its a usable close range weapon. Still the shotgun needs modification or a complementing weapon to really find its home in the fight. Fire rounds are usually the best choice due the their anti armor and harassment potential.
2. Max Accuracy - Fire rounds: This weapon has enough range and versatility to be used as a primary for most situations. It has a tight enough spread to land hits against infantry at long range and inflict the fire status effect. This can be effective harassment against any player target. Within the closer end of mid range, it can deal serious damage. Often mortally wounding foes with 2 or 3 shots.
Up close it can score a 2 hit kill on even heavily armored foes. The fire rounds deal plenty of shield damage for this. The real trick is actually hitting them. Putting your target in your sights and pulling the trigger is not enough. More often than not, lag will force the shot to miss at close range. Locking on is a great way to score a decisive hit but thats only a temporary fix. The best way to land hits is to ambush or fight in narrow areas. If they don't have a great deal of vertical or horizontal wiggle room, your chances for a killing blow are increased dramatically.
This set also deals considerable damage to vehicles and turrets.
3. Max damage - emp rounds: This is an intersting if gimmickey set. This weapon is actually able to one shot more fragile targets but only at point blank range. Think of it as a halo shotgun. The reason it uses emp rounds is to take advantage of the slowing effect for follow up shots. At close range (but not punching distance) it deals significant damage to infanty and usually assures a kill. Its wide spread negates the aiming trickery of the accuracy set (mostly) and makes it easy to jump around and still score hits.
This is a situational weapon. Its virtually useless at anything but close range. If you plan on kicking in doors or holding a base then this is a good choice. If you are doing any work out in the open then you need a complimentary weapon or another class entirely. Even though it is a limited weapon, Its the only one I know of able to score kills with one trigger pull.
The accuracy shotgun and the power shotgun are very different animals. The accuracy shotgun is good out to mid range and can work effectively as a main weapon. At range it is virtually mipossible to avoid unless your target has cover. If they have cover then you must reposition yourelf to get around it. Every inch of avatar that is behind something reduces your chances of a hit. If they have good cover then its virtually impossible to win over any weapon, even up close.
The power shotgun is essentaill a big fist. It can deal massive damage in its element and its spread is wide enough to help with aiming...to a point. Any more than a few yards away and you are better off with something else. A handy tool for specific situations. Avoid open combat.