Wow..you have come up with interesting nominations. Juhi Chawla has always been known for her smiles and giggles. So she is a winner here. But Katrina and Genelia also have cute smiles. Katrina has more of a tight lip smile which gives her a second or third position. If I have the liberty to think beyond this four, I would give my vote to the angelic smile of Vidya Balan.