My favorite cards are:

Shark Typhoon - By far, my favorite one. It has a great flavor and it is playable! :D

Yorion, Sky Nomad - because you can't lose if your deck has more cards, right? Right?

Gyruda, Doom of Depths - I think its true power is yet to be discovered.

Luminous Broodmoth - great entrance animation!

Neutralize - A counter spell with cycling? Great!

Valeera is a blood elf. :)

https://wow.gamepedia.com/Valeera_Sanguinar

Same here...

Completing a quest! :)