I personally like planks and in-and-outs. I find these also work my abs very well:
But most important is to eat clean! You can work them all you like but if you don't eat right you'll never see it pay off!
Drink lots of water. I've just been drinking only water, coffee with coconut oil and coconut milk, or green tea as well as detox teas following with lots of water. Just cutting out any sugary drinks, food dyes or artificial flavoring I've lost weight.
*Drink a full glass of water before you eat it will help you get full faster also eating slow helps too.
300 Core, my own recipe .. Enjoy. Do as much as u are capable, don't over push, if they are easy, add in some weights gradually..