Verified answer

Crunches will do nothing for you. They are amongst the most useless exercises.

Running will burn the most fat in that area than any other exercise.

Keep in mind that long distance running is the absolute worst thing one could do for muscle growth, but with that being said you should get some sort of cardio in to help gain that definition. Also your going to need to be doing more than 100 crunches a day. You are going to need to do different core excercises, because crunches only work part of your core. Throw some planks, invertedsit-ups and ab wheel (or other core excercises if you don't have the proper equipment) in there where you can.

Crunches and other ab exercises won't give you a flatter stomach. Like any other muscle your abdominals will grow when you stress them. If you want those washboard abs a lot of it is just good genetics. My abs pop out a bit because I used to work them out so hard. I don't really care because I've got a steel gut now.

If you want to have more defined abs then your bodyfat needs to be around 8%. Cardio is key for lowering overall body fat. You should also train your lower back and obliques. Just doing crunches won't target all the core muscles. Remember that the chain is only as strong as the weakest link. Plus if your abs are overdeveloped but your back is lagging it could affect your posture. Look at guys that work out their upper body but neglect their backs. They tend to hunch.

Personally I think you should just be happy with what you've got.