Assurance or Payback? What's the Difference?

Question

Just from the description, they seem like they both do the same thing. Power of 50 if you hit first, doubled power if you just got hit, right? But I've been hit with Assurance after hitting the opponent before and it didn't seem anywhere near that powerful. I haven't run into any Pokemon knowing Payback yet to compare. I'm trying to figure out which one, if either, I should teach to my Umbreon. Your input is much appreciated. :)

Answer 1

Assurance does double damage if the Opponent took damage the same turn, like if your team mate in a double battle hit the opponent before you did.

Payback does double damage if the User was attacked first.

Defiantly give Umbreon Payback. Curse+Payback on Umbreon is an amazing combo that is frequently used.