Its simple. The rule of thumb is that standard can deal with all suits even the tryhard officer ones. Advanced and proto shotgun when you don't have confidence in your aiming or its a heavy getting reps. Just dance and rack the lever.

IMO, Shotgun is a little too good in some cases. I kind of wish there was more of a gap between STD/ADV/Proto as it feels a little cheap getting one/two-shotted by a militia or standard Shotgun. Per shot damage is high among all of them (480 at standard, 509 at proto, if memory recalls) which sort of curtails progression a little bit. The difference between a Standard Shotgun and a Prototype Shotgun is a 6% difference, whereas most other weapons are a bit higher (AR sits at a 10% difference from STD to Proto, Sniper Rifle is about a 9% difference, and the Nova Knives are a whopping 67% difference). That and 28 damage worth of difference only really matters in fringe cases, but another shot - even glancing - would be enough to put the target down anyway.

I totally understand if you get the drop on someone but it is slightly unfair for the person to not even have time to react or shoot back in a face-to-face fight, even at the standard level. Starting out, if you miss, it should be punishing. That's the nature of high risk/high reward and I think the lower tiers are a little too forgiving.