Oatey 43653 4" Cast Iron Twist-N-Set Closet Replacement Flange

Cast Iron Flange is the way to go

I tried a PVC flange in a recent repair and trying to wiggle it into place... it was a chore, I even greased it. But when I tried to hammer it in, it cracked. Had the same tightness problem with the cast iron unit, but it took the beating a little more.