What's the better character card deck set, Thief or Pirate?

By the way, isn't the warrior set useful too?

Kinda depends what it's added to. Even on a character with 99,999 hp, 10% HP to damage is only 10k damage. (although that does bring up an interesting point if you stacked 2 warrior sets on an HP warrior). Most classes are more like 8-10k HP at high levels, so maybe 800 damage per hit.