Seated hamstring curls are preferred over prone hamstring curls for isolating hamstrings because they maintain greater tension.

“my favorite is a seated uh hamstring curl and the reason for that is um it is better able to isolate your hamstrings than say a prone hamstring curl where you're in the uh you're laying on your stomach and you're kind of curling the machine in towards your hamstrings and part of that is just because of the position of the movement”