It really just depends on the Pokemon and its stats/moves :)
If you see the Pokémon of the Day and Week in www.serebii.net ,you will see the recommendations for contests,battles,natures...
action replay is best
Your best bet is to capture more Pokemon cause that increases the chances of winning a lottery contest for jubilife city. P.S You can get a xp share and a MASTER BALL!!!
aura sphere is really cool i wonder if it would work well in a contest
you need to feed pofin to your contest Pokemon
Feed best pokeblocks to your pokemon, Teach best moves for the contest your entering and just use the right moves at the right time.
i depends what moves you teach which Pokemon, but i would recommend a kyogre with surf, hydro pump, water spout and dive. i repeatedly won the master rank with it.
Personally, I love them all. Strongest - Bidoof/Bidoof Quickest - Magikarp Best defence - Starly Hope this helps! the Pokemon master pokemonseeker012 changed answers IT'S FUN
Chris Doucett is the best Pokemon Master because he caughtem' all.
Diamond is not a Pokemon but i think Arceus is one of the strongest Pokemon ever.
the best Pokemon on diamond would be arceus but you can only get that from action replay, other than that i think the best Pokemon would be giritina..
the best Pokemon for the Pokemon league is definetly latios