There are two energy shotguns. Well, sort of. The DCM-8 is an energy shotgun, and the Banshee is technically a "Sonic" shotgun, but it would be easy to mistake it for any other energy weapon. The only differences are that it doesn't automatically transfer ammo from your stock to your active mag without an attachment (or one specific variant), and instead of Long Barrel or Particle Amp, it gets a unique attachment called Speaker Amp. Anyway, the DCM-8 is pretty underwhelming, and the Banshee can take a bit of finesse to use well. It has middle-of-the-road OSK range, but a considerably better pump speed than the other two pump-actions.
If you want an easy shotgun, go for the Reaver. If you want fewer hitmarkers, go for the S-Ravage. Either way, you've got to get in pretty close to do good damage with these shotguns, so use sliding to your advantage.
Laser sight is a good tool to make your shots more consistent (hitting every pellet counts for a lot), though it can also make it easier to get a full miss if you're off target. Long barrel doesn't provide much of a range boost, but if you're looking for every inch you can get, that's something. Similarly, suppressor doesn't cause too much of a range nerf, while being a powerful tool for getting multiple shots in without tipping the enemy off too quickly, and keeping you off the radar.
And like kuYuri says, the Lance variant for the Rack-9 is one of the few variants that makes the weapon worthwhile. Unfortunately, it' also costs 2,000 salvage to craft. If you ask me, I think it's pathetic that any worthwhile spread-tightening has to be part of a variant when it's mentioned as a feature in the base weapon's description.