There isn't a strongest (unless all the Pokemon are level 100). It just depends on the type, the moves, the size and the level.
another answer:
yea there is if theyre all at lv100 with all moves that they learned on their own. it is lugia, bcuz even in the pokedex entry it says lugia is the most powerful.
Actually Arceus is since it can learn almost every move in Pokemon history, including roar of time!
Darkrai
the strongest Pokemon is arceuse
Some of the strongest Pokemon trianers in Pokemon diamond & paerl
Diamond is not a Pokemon but i think Arceus is one of the strongest Pokemon ever.
arceus
By leveling up your Pokemon from eggs.
shier piller
ARcues
I think arceus is the the strongest Pokemon in diamond and pearl. Also no moves are supereffective on Spiritomb and arceus
the strongest Pokemon are Salmence lv100 and Slakazem lv99 i should know because i have beat the Pokemon league 4 times only with these 2 Pokemon.
In Pokemon Diamond i say Torrterra is the strongest grass and ground Pokemon because i have a level 100 one and it's great.
when you battle Pokemon champion Cynthia in Pokemon pearl,platinum,and diamond her strongest Pokemon is garchomp
Torterra and Golem are a few good choices