I think a Champion that uses Pre-Evolved or monsters that don't evolve at all would be good.
Pretty easy to beat unless Nintendo/Gamefreak allowed them the base stats of their fully Evo'd family members.
I don't think an Eevee Champion would be a bad idea either, with all Eeveelutions except Glaceon.
They'd also all have Hidden Power to cover their most potent threats (Flareon would have Grass for Water and Ground types for example).
The Eevee master would be female and have massive pig tails (Like the trainer from the Black and White anime series).
That's all I got.