This thread comes a little late for me, since I have the Japanese version of Platinum. XD
But my Japanese team was...:
Empoleon, Garchomp, Espeon, Staraptor, Lopunny and Luxray.
I completed up to victory over the Elite Four with the Pokemon mentioned at Level 54, Level 55, Level 53, Level 53, Level 54 and finally... Level 53, respectively. I admittedly used Garchomp for most of the battle against Cynthia, due to her weakness to Dragon and Ground types in her hard-hitters. As for why Espeon rather than Glaceon... I wanted a Psychic type, but didn't want to use Chimecho or Alakazam. (the latter being the previously most-used in playthroughs, for me)
As for when I purchase it in English... Hmm...
I'll probably go with Torterra, since I've used Empoleon in every playthrough, thus far. Glaceon will also be a Pokemon I will use in my English playthrough, but I'll likely trade to my Diamond Version so that I don't have to wait until I get to Snowpoint City to evolve it, and actually get a suitable Ice type attack on it. Area evolutions are a real pain when you've not got that far, yet...
As for the rest... pending. I'm not entirely sure what other Pokemon I'll use. But since I used Garchomp in my Japanese playthrough, I won't be using it in my English playthrough.