Garruk and Elspeth are my favorite Planeswalkers.
Garruk is a total Beast!
I've played mostly with Primal Hunter and all of his abilities are insane. Offense/defense by summoning Beasts, card drawing ability (targeting
Primeval Titan is no joke), and his ultimate is just wow.. it's hard to keep a straight face on when you're attacking for the win with a mass of 6/6 Wurms lol.
Elspeth is appealing to me as she's a badass holy righteous warrior Knight commander lady.
I've played mostly with Tirel and have really only used her top 2 abilities. Casting her at the right time, summoning 3 Soldiers, and then successfully protecting her with them for subsequent turns is truly something special. Left unchecked, and paired with other shenanigans like say
Gavony Township or
Mentor of the Meek, her army is definitely a force to be reckoned with.
Honorable mention goes to Jace.
I missed out on The Mind Sculptor so I've never experienced playing with his madness, but Beleren and Memory Adept are crazy fun to play with as well. Milling your opponent for 10 right off the bat, and on subsequent turns if Memory Adept is properly protected, is incredibly absurd. I was never really one for milling, but winning with Memory Adept's middle ability is inspiring and instantly reminds you that hit points aren't the only way to lose.