A lot of it is opinion But there is some factual data that supports a bolt/plunger rifle to be more accurate and consistent. A free floating barrel for one thing.. BUT I know of many break action rifles that shoot very very well, less than 1 moa typically with the right load.
I Currently own 26 muzzleloading rifles..only one is a break action..it’s a cva wolf. It’s cheap enough I use it as a loaner rifle so I don’t have to worry about it getting beat up or Damaged..I’ve owned optima’s, encores, and even one traditions break action..the encore had the best action in my opinion..the rest are very clunky feeling..and they don’t handle very well.. my black diamonds handle very well as well as my knights…
Now I gotta say if I had to choose one action and one only..it would be the drop away breech from The omega platform..after all the omegas are half of my stock of rifles.. short profile, handles like a rifle, free floated barrel and super easy to clean. Hands down the best design in my opinion for an inline rifle