We collect Amiibos because they are very cute. We finished Yoshi's Wooly World around Christmas, and I thought an Amiibo would be a very cute thing to commemorate the occasion. My boyfriend already has the green one, so I decided to get the pink one. I know it's a matter of opinion, but I think the pink one is a lot cuter than the blue or green ones. He's very excited about this one as well.
Since we collect them, we haven't used them for any gameplay. From other people I know, I have heard that this is a great addition to single player games in Yoshi's Wooly World. I, however, cannot attest to that.