Low bodyfat is definitely a must, but I don’t go so much by getting to a certain b.f. percentage because as others have mentioned, how you store your fat is a lot of it.
For example, I was training with a friend of mine about a year ago and I tested his bodyfat. He had very even fat distribution all over, and although he was at 11 percent and I was around 7, he actually looked just as lean around the midsection as I did.
For competition-level abs, it will generally require getting the skinfold down to 4 mm. give or take. Best I’ve ever done is 6. That record WILL be broken in the Inferno Challenge!
For me, I store fat predominantly in the abdomen. I also have short, tight hip flexors that contribute to protruding lower abs and need some addressing as well (working on it). Right now I have full vascularity (or “veininess” as one of my buddies calls it) virtually everywhere on the body but the abs are still needing some work.
And having strong abs definitely helps…if you’re not using some good resistance on them, you won’t get the full cosmetic effect. Doing sets of 100 reps on crunches isn’t going to do jack.
I always laugh when someone comes into the store and wants to lose fat and says something to the effect of, “but I already do sit-ups and crunches for two hours a day, seven days a week and I still have a gut!”