I do both, i do decline situps with the plate 'standing' on my chest.....
They work undoubtable, and are in ALL ab sessions...
But those heavy ass crunches, seem to leave me sore as shit for days in the abs section. Very good for MAX ab days. But no way in hell could u do those 3x a week...(as some people here do abs 3-4x week)
Now jpt, rope crunches = kneeling with the rope behind head and crunching??
if so thats great because i do them with the bands in this fashion