Space Break > Time Roar
High Crit. 100 Per Turn or 150 for 2 Turns?
Steel/Dragon is a good type, but Dialga looks like a retarded horse. I can't possibly see how it can use Dragon Claw with its hoove.
Palkia has wings and is the first major legendary in a long time that has FULLY formed arms, unlike Rayquaza with the little claws, or Lati@s with the retractable arms, or the numerous birds, or the numerous quadrupedic legendaries. Either way, Steel is a horrible attack type, but good defensive type. Water is mid-way on both, so Palkia is better suited to sweeping rather than Dialga is. Dialga IMO would be good with CB to Time Roar every once in a while, but otherwise I just don't like it.