You do realize that Dialga's type matchups cause it to resist both of Palkia's STAB moves, not to mention hitting a STABed supereffective hit on Palkia with a dragon type move. With that said, Dialga wins in a head on match against eachother. I haven't the basic knowledge to really judge them on their power and effectiveness because I've never used them before. From what I do know, Palkia is stronger because it hits faster and gets powered up in the rain. Palkia looks better than that freakish temporal giraffe. Palkia wins my vote.Palkia would be a bit stronger than Dialga, due to it's Type Matchups. Although in the terms of their actual movesets, Dialga rules.
I prefer Dialga, anyways.