ultimately it depends on how much dampening you want and how much money you want to throw at it!
we used Rockwool throughout and standard 12.5mm plasterboard on both sides of internal walls. we do get sound transfer but then again, it's a house and not a museum so we don't mind a bit of transfer. besides, more often than not doors are left open so no amount of sound insulation is going to fix that! 🤣
i'd suggest RWA45 personally. nicer to work with than the Isover stuff afaik and it stays in place between the studs well.
we put 50mm in the walls and 100mm in the ceilings