Alfred, cylinder or improved cylinder usually gives best accuracy. Don't use anything less restrictive than modified for slugs. Have a great day!

Alfred, you will get the best performance out of cylinder and Improved cylinder chokes. You will have to test different slugs threw the two chokes to see Wich gives the best accuracy. Hope this helps.

****Oops rifled chokes, are supposed to improve accuracy

Modified, improved cylinder will both work, but out of my berreta I usually just use the Cylinder bore choke.
They make rifled chokes as well. I don't currently own one, as i don't shoot many slugs ( they are spendy and hard to find right now) but the rifled slugs are supposed to improve e accuracy a little bit.

Alfred, this would be the least restrictive choke Sir which should be Cylinder/Improved Cylinder. Cheers and stay safe!