Best EX: Mettagross. In my opinion, mettagross, flygon, and skarmory are the only good ex's.
Best Trainer: Steven's Advice/_______'s Stadium
Best Pokemon: Blaziken
I'm certain at all, but the best for each group for me has to be:
Best Ex - Absol Ex/Flygon Ex/Skarmory Ex
Best Trainer - Steven's Advice/Battle Frontier
Best non-Ex Pokemon - Gardevoir/Blaziken/Delcatty/Magneton
The best overal is probably Gardevoir for me, but I'm not certain.
EXs: Salamence, Shiftry, and Flygon. They all can have a good use. There's nothing special about Claydol, though.
Trainers: Steven's Advice.
Normal Pokemon: Gardie, Magneton, and Machamp.