Depends on application.
I have had quite a few different fixed 4x mounted, some fixed 10x and some 2-7x and 3-9X scopes.
When tuning up the different k31s for accuracy, I like using the 10x Bushnell Tactical so I always have enough adjustment range from one rifle to another. I just un-clamp the mount and move the whole mount assembly to another K31 to tweak up the action and barrel band screws. Minimizes the ammo I use.
Favorite 4X is the Zeiss Diatal C. Great in the bush. Can resolve blades of grass and leaves much further than one would think possible.
Others, Bushnell 4x and Nikkor with posts. Ok for hunting where fast shots are needed.
The Zeiss I can use for accuracy testing even with just the 4X because the resolution is excellent
Not so with the 4x Bushnell and Nikkor..
10X Bushnell 10x 3200 tactical. Very good, past 100yds. Parallax is a problem under that.
10X Redfield(old), Can be sharp, but takes forever to focus to get it sharp due to short focus waist of the optics.
12X S&B, tried it once on K31

, but reserved for the SSG PII.
Bought a Nikon Prostaff 2-7X32 rather recently. Decent optics for the money. Using it on the 96/11.
Still trying to find a good straight tube objective scope for the K11 which has the iron sights right where the the scope bell would be situated. Hoping to find some AR type scope with small turrets and no drop compensator reticles which will get in the way.