Sit Ups vs Crunches, which are better?

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Please help settle a debate between my hubby and I, which is better for you to do, Sit Ups or Crunches? I say crunches because sit ups put stress on your neck and back and about halfway through the sit up (what would equal a crunch) your hip flexors take over anyways and you abs are no longer doing the work. He says this is a bunch of bull, if done properly there is no stress on your neck or back and people just use this as an excuse to do crunches instead because crunches are easier. He thinks crunches have no effect. I know you have to do cardio to burn away the fat to even see the muscles anyways, but doing crunches is still part of my exercise routine to help build the muscles and tone my abs, along with the cardio. Which do you think is better?