Quoted By:
For me, it's the Treecko line.
Instead of just being different for the sake of it, their Shiny color palette actually adds to their coolness and makes them look even rarer then they (supposedly) already are. I'd imagine they'd belong to the kind of Shiny Pokemon that Pokemon Collectors in-universe would pay a great amount of money for.
Just my opinion, of course. But to me, they are perfect.