Platinum; this was without a doubt, yo.
The health bar layout looked WAY better D/P not mention the opened Pokedex and being able to train Leafeon and Glaceon...I mean, damn...why weren't they in D/P.
The torn world and the extra battle with Cyrus, Mars and Jupiter...not mention the revamped storyline...
...The rematches with gym leaders...and finally the battle frontier. There's prolly more, but this is all I can think of.