Actually, you have to get the Master Rank ribbon in all Contests - Beauty, Cute, Cool, Smart and Tough - to get a star on your Trainer Card. I've almost finished this task; as I have them all but Cute. I don't know about you, but for me, the Pokemon I chose were:
Cool - Groudon
Cute - Snorlax
Smart - Gardevoir
Tough - Tyranitar
Beauty - Dragonite
They all work very well for Contests; especially if you have the right movesets. I highly suggest these Pokemon. Good luck with your Trainer Card!