The M1216 and S12 just seem to work better for me in both Core and Hardcore modes. They put more shells out and have more chances to redeem yourself if you miss (in Hardcore.) The KGS is terrible in this department... Remington isn't so bad.
i learned a ton by going to my call of duty elite weapon performance. according to the stats elite shows my k.d in this order
Pretty huge drop to the KSG, but i expected it because it is definitely the hardest to use due to having to be dead on with the slugs. That being said my actual preference goes something like this
the r870 is my most used weapon and highest kills according to elite. i love the KSG because its just so satisfying to actually get a kill with and the range on it is beastly.
the weird thing that i never realized is that 291 out 599 kills with my S12 were headshots! thats almost half of the shots. i would have never guessed. i make be breaking that one out to try again. i have my shottys diamond but i need to 2nd prestige all but the R870.