The Eviscerator is a very good general-use shotgun for Vanguards. Lightweight enough that it'll eventually leave them at 200% cooldown once it's ranked up, good ammo for a shotgun, good firepower, and no real downsides. The Krogan can get away with heavier though, especially if you took the rank 6 class talent that decreases shotgun weight. Mine uses a Wraith 1 and is at 190%.
I wouldn't put an Eviscerator on a caster myself, since unlike Vanguards, they don't generally want to be in close to their opponents. Maybe a Fury, Shadow, or Asari Valkyrie, but I don't have any of those yet.
Zevox