Sarkhan, the Dragonspeaker Sarkhan Vol is my favorite planeswalker because his character is sweet and because he interacts with your opponent in multiple ways
Some decks can be built around the cascade mechanic, as there are ways like Yidris, Maelstrom Wielder to give expensive spells (like the ones with landcycling) cascade
This is one of the most reliable offensive dorks you can play and sits nicely at the other end of the spectrum to Hornet Queen
Finally , you can put a Simic Birthing Pod in the command zone
Its a viable land in a bunch of eternal formats (I'm looking at you, Dark Depths) and everyone should own at least one copy in my opinion
Adding more value to him is the fact that late in the game you can transform him and either dig for more resources, blow up any creature/planeswalker or recur something from any graveyard