I hunted in a slug only area in MI for 15 years. In that time I used irons, 2.5x fixed, and 4x fixed.
If I did it again it would be 2.5x, 1-4x type, or a red dot. Back then, hunters used red dots but they were not nearly as user friendly as they are now. Being able to leave them on for years being the strongest factor.
I still have a rifled slug gun I used as recently as last year and have a Leupold 1.5-5x20 Vari-X III on it. Works great.
My main criteria for a slug gun scope is eye relief if you are using a 12 ga and a modified bird style shotgun. 12 ga recoils hard enough and if you are using a shotgun which was originally designed for shotgunning, it is usually I’ll fitting for slug shooting with a scope and tends to recoil further back into you. Scope eye is a real consideration with scoped slug guns. I like at least 4” of eye relief. 20 out of 21 scopes out there have close to a 3” eye relief. It pays to find a shotgun (or hard recoiling rifle) specific scope.
If you have a 20 ga or specialized slug gun like a Savage 220/212 or H&R Ultra Slug Hunter or Remington Special Purpose, the need for long eye relief is diminished.
Red dots with unlimited eye relief are also a great option.