My favorite would be
Elspeth Tirel and all versions of Sorin. Token generating, lifegain, and destruction of permanents. Sorin especially, can turn a game around with his ultimate moves.
Speaking of favorite planeswalkers, my least liked ones are
koth of the hammer,
nahiri the lithomancer, nissa rivene, tibalt and most forms of liliana mainly because those cards require a deck built around them for the most part. I know a few will say all planeswalkers need a deck built for them, but those few seem restricted to work only in tailor-made decks for them. For instance koth and
liliana of the dark realms require several mountains or swamps and don't work as well in more than 2 colored decks.
Liliana of the veil has one lousy ability, one okay ability, and a great ability with respect to her +1, -6, and -2. Also you would think one of her forms would have something to do with bringing out zombies or zombie tokens. Nahiri and nissa require artifacts or elves in the same way. Tibalt is just both too easy to kill with a
shock and has a lousy +1 ability. Of those, if I had to pick one that I dislike the most, I would go with the forms of lilana since she has several forms that are just okay excluding lilana vess.