Well Id like to think ALL of mine are strong. Haha. I usually have, post elite four, about 10-15 pokemon at or above level 50. But in comparison to those Im fighting, all of mine are fully ev trained by level 15 or 20, and therefore are stronger than any normally trained pokemon, even if the foes are at a fairly higher level. And I also take advantage of useful items, such as Life Orb, Muscle Band, White Herb, etc. I am an AVID dragon type trainer, and have a plethora of both physical and special attackers that dominate most types, including their weaknessses. But it terms of level wise, since mine are usually lower, you could say none are strong. But by the time I take on the elite four in Platinum for the FIRST time, all of mine are level 60+.
Fave Platinum Team: Infernape, Garchomp, Jolteon, Espeon, Floatzel, and Swellow.
I have access to Emerald and Leaf Green as well, allowing for a potentially diverse team, depending on who Im fighting.