My reason for liking the 'Defender of the Skies' is because it's very majestic! ( that sounds really cheesy! ^_^)
It's a pretty awesome looking Pokemon, and very mysterious. I've always wanted one.
Ho-Oh has always been my favorite of the legendary birds of the Pokemon series, because the beautiful colors on its wings just make it look majestic. And that it has a Sacred Ash equipped is pretty awesome as well.