My top four favorites are the only 4 that I own.
Jace, memory adept...
Liliana of the dark realms....Garruk the relentless...and
Chandra ablaze. These guys (and gals) are like my fantastic four of the magic universe. Jace mills hard with his plus 0, mill 10 cards. Liliana was the first planeswalker I ever got, she's attractive, her skills are
dangerous and she completes my black shade deck marvelously. Garruk is the coolest because his transformation takes extra care and practice to perfect which makes me really focus on his deck construction (also the black wolf tokens are awesome too). Lastly
chandra ablaze is just fantastic. I could just keep dropping her phoenix in the grave for her effect and just add it right back to my hand. And to use all my red burn spells from the graveyard in any order i choose....red hot victory on a plate.