My opinion on that matter is that the more pellets you have to begin with, the less you’ll benefit from two extra pellets. The initial accuracy also plays a big part, since you want ALL your pellets to hit. If the accuracy is low, then those two extra pellets will be like putting a wedding dress on a pig. Useless! Critical prefix makes the spread a bit tighter.
Unless you’re at point blank range, you’ll never hit with all the pellets anyway if you’re using shotties with Bandit or Torgue barrels, and if you’re close enough to actually land all those hits, then you’re close enough to land them in the crit spots, so I prefer the critical prefix on these.
Jakobs barrels are somewhere in between, but I usually go for extra pellets there.
When it comes down to Hyperion barrels, the extra pellets is usually the best option, simply because you alreday have good accuracy on those, and therefore want to land a few extra hits on each shot.
There are exceptions to all this for certain situations, but this is my rule of thumb.
CC is different in that aspect. The Interfacer (and a few more guns) have a “sweetspot”, which means you’ll have to be at a specific distance when firing. The CC has a special effect that repeats itself as the initial burst travels. Stand in a corridor, or alongside a wall, and fire your gun. You’ll see that the intervals of the burst to the side changes when you spec in Velocity. Same thing with Accelerate on Maya. This means that, in order to get the maximum dps, you’ll have to be at a distance that matches one of these intervals when you shoot an enemy. Bottom line is that you can get the maximum damage output from the CC from several various distances. On the Interfacer it’s one set distance.
Whether it screws with a gun or not is still up for debate from time to time. Me… I prefer to NOT spec in Velocity or Accelerate when I use guns with a spred pattern. But some do!