I also learned that working the abs just does not have to take place on the floor doing some crunches. As a mater of fact I have heard some personal trainers say they have totally ditched crunches. Working the abs standing up, is very beneficial especially for the obliques. While planks at first were not a favorite exercise as you excel you will find that they are very versatile, and a great over all core work out. Planks is what some do alone for ab work, while they are great for the abs they also aid in strengthening the back.
Personally I like a combination of all the varieties, crunches, stand up abs, and planks. Everyone is different you need to find what works for you in creating the great abs. I've never had six pack abs, but that is okay I just want my abs to look the best they can for my body.