It's all subjective which is what makes it so interesting. Amy has a brilliant voice which a huge amount of character, Whitney has so much soul and power behind hers.In terms of songs, Amy's are amazing. They're all very auto-biographical and really compliment her very unique style, which has become rather iconic over here, especially in areas like Camden.
I suppose I connect more with Amy because I experienced her at her best where as with Whitney I wasn't really around to experience it. While I can appreciate both, Amy is the one I'd prefer to listen to. There was also the progression in her music, with her darker life events really reflected in Back to Black.
So for me, Amy Winehouse > Whitney Houston.