Cast Iron or PVC Flange?

I need to replace two flanges. Is PVC better than Cast? Are they had to get in the cast pipe?

The strongest one would be a cast iron one leaded into th eold stand pipe. There are some internally expandable versions that basically clamp onto the pipe that would work. Probably other choices...one of the pros would have some thoughts.

flange

The couple of insertable ones I have tried to use on cast iron, had to be trimmed, then beat into the pipe, and even then they would not go all the way down to the floor.