I think the High Wall is the strongest of the actions mentioned, the Sharps is probably the least strong, in part, due to the off center hammer. As to which is best, it'll depend on what you want it to do. You can get Browning High Walls in modern calibers, but none of the others are anywhere close (the Low Wall is just a High wall adapted to smaller cartridges, so you can reach in there better). If you plan to shoot black powder, all are sufficient for that task. The "cool factor" of the Sharps can't be ignored, but the others are probably better for hard use.