Classic: G. U. N, Prime, Glitchpop

Shorty: Oni

Frenzy: Elderflame, Glitchpop, Prime

Ghost: Sovereign

Sheriff: Reaver, Ion, Singularity

The fact that half of the pistols have 3 skins and half have only 1 is poor distribution on Riot's part. Before late Act III, the Ghost was the second most popular pistol round pick. Also, the shorty is the only skin in the game without SFX for the skin, unless you count the Oni kill noise.