well the arceus event has now been anounced to be in the us for pokemon platium soonI'm not too fond of this trio, and even if this event occurred in my country, I wouldn't go. But outta the three of them, probably Palkia. I'm too lazy to catch one in Platinum, and I don't have Pearl, so go figure.
You dont have to catch it you just get given a lv100 arceus by the green man in the martthis does not really matter to me also, because i may not be able to catch arceus anyways, but i would pick dialga, because i have not used dialga yet