I love both, but Chanel Chance is my favourite, I think its a bit of a younger scent, Plus my boss wears Coco Madmoiselle and I swear she must use at leats half a bottle a day, because anywhere she goes you can smell it 20 minutes after shes left and I work in a massive building!!!
I do love Coco Madmoiselle though both are really nice fragrances ( and they have quite similar notes ) but I just prefer Chance, always have.