There really is no "best" or "worst" plates. it will depend on:
HOPE I HELPED!!! <( '' )> <--------- = Kirby!!
Arceus (With Dragon plate)
You can search on youtube. that's where i found mine.search Pokemon PLatinum plate locations.
there is no such thing as a "Curse Plate."
Underground!
you can get iron plate by using explorer kit
a fist plate
purple
you have to dig it up when you are underground
if a Pokemon holds a plate (arceus) and a Pokemon uses flail the shards restore the plate because flail breaks the plate.
no there is no such thing as the polychromatic plate
try your best to find spirtomb in Pokemon platinum
Steelix