In my opinion the best way to get good corestrenght is properly done squats and deadlifts. The best way to look good, is to train hard and eat right. Ive never done abs since i was like 18 and had to do it when it was a part of the martial arts training. Doing abs is unnessesary and doing a lot of exercise for the abs is a common mistake beginners in the gym do. Or veterans that to stupid to go to the library and read some books about training, nutrition and related things.
Hate it when people come and tell me that they are going to get fit untill next summer, they are going to do a loooooot of situps. Gah. It seems like lazynes is very comon when it comes to people talking a lot about training and wanting to get fit a lot. Lazy in that way that they can spend so much energy on what proteindrink or aminoacids or other supplements they should eat, and extensive talking about their training, and in some cases even a lot of work in the gym. But still, to lazy to go read a book about basics in nutrition and training. And the results, well look around. How does people look and how does people want to look?
Listen to people that know what they are talking about, if you listen to top bodybuilders there is a risk thou that you are talking to someone with genetics that 99% of us do not have and therefore they are not the best to get advices from if you are not like them. But good old facts, in books, in the library.
Also i fun book to read is the 4 hour body