I'm surprised this wasn't made yet.
First, we have...
Diamond's Steel/Dragon mascot, famous for its mastery of time, a sturdy build fit for a tanking role, and the destructive yet dicey Roar of Time.
Next, we have...
Pearl's Water/Dragon representitive, revered for its ability to warp space, a higher Speed which makes it an effective sweeper, and the reliable Spacial Rend.
And now, the usual questions.
So, which one do you prefer?
Which one would win in a battle?
Which one is more useful?
I prefer Dialga. I've always liked blue as a color, and I'm more into time than space. Also, one popular meme fits the head of Palkia: PINGAS!