Why not do both? I train abs 2x a day about 5-6 days a week. I am training for strength right now...so I train heavy with abs. I have never trained abs consistantly....till now...in prep for my contest.
I never do high rep, pretty much always resistance unless I'm so totatlly fatigued I can't even handled adding weight too any of the movements. I train em like any other muscle. Can't stand high rep.
Favorite is the roman chair followed by decline then leg raises.
i love to start with 6 sets leg raises or crunches
i follow up with 3 sets roman chairz and cable crunches.
I use weight that allow 10-6 reps, but i drop the weight twice to extend the set to about 30 reps this counts as 1 set. This will give you the density AND the refined look provided your BF is below 14 %
do both. key is focusing on the movement, it doesnt have to be big. Vrunches work great with numerous variations. But so do resistance exercises like cables.