Ok here is my top 10 that I play with the most. In no particular order
Sarkahn the Unbroken
Huatli, Radiant Champion
Nichalos Bolas God Pharaoh
Koth
AJ 3
Saheeli
Garruk
Lil 1
Angarth
Kiora
Honorable Mention
Vivien
Nissa Worldwaker
Jace 2
Samut
Sorin
Nahiri
Ral Viceroy and Teferi because I’m just started to use him
OB
Best Monocolor Walkers:
Best Multicolor Walkers:
Sorin, Angrath and Ajani Vengeant almost make the list. Saheeli would make the list if it were “Legacy Only”. I think Nahiri is overrated - she’s good, but she’s not Top 10 good. I also think Ajani Unyielding is underrated, but he, too, is not Top 10 good.
Three special mentions for walkers I use a lot but don’t necessarily recommend: I use Samut a lot, but oddly, do not really consider her a great walker (she’s basically just double-strike on a stick); she is, however, great for some “win in X turns or less” objectives and just generally saving a lot of real-life time in PvP matches. So…not a great walker, but kind of a great time-saving device, I guess? I also don’t think it’s worth the runes to level her past 50, for whatever that’s worth. I use Garruk a lot, currently, but I have a strong suspicion that when Ghalta rotates out of Standard I will go back to using him almost never. And I also use Tezzeret 1 on occasion (for Legacy), but just like my usage of Garruk is basically entirely based around Ghalta, my usage of Tezz 1 is entirely based around Omniscience. Without those specific cards I wouldn’t really recommend either.
I own all the walkers that have ever been made available for crystals, but some I have not yet leveled up: Domri, Dovin 2, any of the Lilianas except the 1st one and Death’s Majesty, Gideons 2 and 3, Chandra 2, Huatli 1, Kaya, TED, Jace 1, Jace 3, Nissa 1, Sarkhan 1. A few of them I specifically haven’t leveled because I think they’re bad (lookin’ at you, Chandra 2), a couple I think are probably good but I just haven’t gotten to yet, but for the most part, no strong opinions about any of those.
I just finished leveling up Tezzeret, Master of the Bridge and honestly can’t decide whether I like him yet or where/how I’d rank him. He’s been underwhelming me but I sorta feel like maybe I just haven’t gotten him a deck that quite clicks yet.
My list for current standard (not exactly in order):
Sarkhan3
Bolas1
Tamiyo
Teferi
Kiora
Huatli2
Vraska1
Karn (PvE MONSTER)
Ral
NB2
Best Mono (in no particular order):
Gideon Blackblade
Jace2
Nissa Worldwaker
Ob (though I don’t use him much anymore)
Koth (also don’t use him much)
Elspeth
For Legacy, Saheeli, Tezz2, and AJ1 are amazing. AJ1 still is rock solid in standard, but not as great as he is in legacy. Other walkers I personally really like but can’t quite call top tier are Samut, Nahiri, Domri, Angrath, and Dovin2.
A few walkers like Angrath and Jaya used to be among my favorites, but they have both been nerfed since they came out. I could see Jaya being amazing again if red gets more strong spells once standard rotates.
However, something @bken1234 mentioned above and a few others have hinted at is REALLY worth considering - your playstyle and to a degree collection make a BIG difference regarding which PWs make the most sense for you to use in any given situation. Where you fall on the Aggro-Control axis for your ‘natural’ playstyle makes a big difference.
My top 10 (all at level 60)
My top mono PW:
For newer players, get Karn (colorless) for PVE, Nicol Bolas Ravager/Arisen (red/blue/black), Sarkhan the Unbroken (green/blue/red), Tamiyo (white/blue/green) for PVPs and you should cover all colors.
My top 10 highest played PWs are:
For new players, I’d advise covering all 5 colors with Nicol Bolas GP and a green-white PW. I went with Ajani Unyielding for green-white, but in hindsight that wasn’t a good choice. GW Huatli would have been a better choice. Covering all five colors with 2 walkers can drastically speed up story mode and your farming of all the gold and runes.
On a side note, Ajani Unyielding needs a buff. His mana bonuses are terrible and his abilities are meh unless you’re in an energy objective event. There’s like one of those.
On another side note, somebody should compile this data and publish it.
10 blue PWs.
Perhaps they do, but I think Tamiyo is #1, nudging just slightly ahead of NB1, Sarkhan and Ral.
Everyone’s list is pretty much on-point, so since we’re now addressing newbies, I’ll throw this in:
As a strategy tip for newbies working on multi-color (or even mono-color, actually), I’m re-stating something someone else said, previously.
You owe it to yourself to have at least one or two supports that will change gems to your color. The later Ravnica “gates” are particularly useful because they will change multiple gems based on how much they are reinforced.
Sometimes it doesn’t work out, but usually with one or two gem changers out there you can end up with some nice cascades before you even decide what cards to play.
BTW, years ago, Sarkhan 1 was my main PW for events and now it’s Sarkhan Unbroken because times change. Red and Black can still be viable (to all those Angrath lovers, out there. 
) but veterans will more than likely play the 3-color because of more selection and they have the cards to win with them.
Finally, everyone was a newb, once. But if you like MTG and you like puzzle quest, stick with it and before long you’ll get your stride. 
I’m going to answer this differently, as I spend the majority of my time mentoring players often from their first week all the way to top 10 or 25.
So obviously, if you’re coming to the forum the day you get the game, spend the crystals and get the 5 Origins PW and join a coalition – you will need your 5 colors covered for 2 reasons – a lot of events have 5 nodes and 2, the 5 Origins PW are designed to teach you the mechanics of each color – you don’t need to max them, just unlock the third ability on each and start using them and working through story mode.
My top 10 list for players in their first 6 months – these are the PW who will help make up for deficits you will encounter in your collection either by limits of 10 cards, or just by limits of small collections and help you be more competitive as you make your way through the tiers and build your collection — in no certain order:
Nicol Bolas, God-Pharaoh (Note: for more advanced players I would replace with The Ravager)
Sarkhan Unbroken
Karn, Scion of Urza
Domri. Chaos Bringer
Ral, Izzet Viceroy
Ob Nixilis, Reignited
Teferi, Hero of Dominaria
Kiora, Master of the Depths
Ajani Vengeant (R/W)
Angrath the Flame Chained
Honorable Mono Mentions:
Gideon, Battle-Forged (Origins)
Gideon Blackblade
Jace, Cunning Castaway (aka Dirty Jace)
Elspeth, Sun’s Champion
Nissa Worldwaker
Jaya Ballard
Koth of the Hammer
I usually also recommend these to new players (except Karn, I think he’s a bit expensive for a newb to only use for PvE), nice list!
I have never seen anyone recommend Dirty Jace for anything, though. What makes him better than, say, Unraveler Jace? I find him to be much more straightforward from a building perspective and much more powerful.
So I didn’t quite understand it either, tbh - but I saw a lot of my top players using silver alts grabbing dirty Jace over Jace 2 and recommending him and gave them both a second look, and I’ve come around on this.
There’s two main reasons I recommend him over his predecessor:
The second though, is even more important:
Jace 2 requires some building to sing. Dirty Jace’s abilities add something. You don’t have to build around him… You can build around him (you even should); but if you aren’t a strong deckbuilder, or you don’t have a very good collection, or you just get bad draws he can do things on top of what’s in your deck.
My list:
Mono-
Blue- Jace, US
Black- Liliana, DM
Green- Vivien Reid/Nissa WW
White- Elspeth
Red- Jaya Ballard (Koth’s weakness to red-poor fields and limited support options has been a an issue to the point that I rarely use him.)
Colourless- Karn
Dual- (in order of opinionated usefulness/fun)
Tri-coloured planeswalkers are very useful and fun, but more for advanced players. I will only recommend Nicol Bolas, the Ravager as the the Grixis planeswalker to acquire and only because there are now three NBs.
I have to disagree.
Maybe her abilities one and two are not the best around, but Tammy does not really need anything special at all.
Even in standard you can build looping decks around three or four rares and rest commons and uncommons.
Of cause bsz does not hurt, but it is also not strictly needed.
Just add some conversion spells, a source of card draw and any wincon like for example beacon bolt and you have a deck that easily wins nine out of ten matches in any scenario.
There’s Ral 
Ral is the bacon bolt king! B)
I do use Ral, and Bolas 1, and on occasion Kiora and Teferi and Nissa 4. But there’s very little incentive to use the weaker PWs in serious events, or even in casual events. I don’t want to cost my coalition points by experimenting with a janky strategy on the weekend and I don’t care enough about the grindy weekday events to spin up new brews for them.
Nissa 4 is surprisingly awesome for a mono green. She can play Killer Instinct decks like an absolute boss.
On the subject of being surprised, tho, I was surprised to discover how weak Kiora was in Standard events without access to decent gem conversion. Still good, but nothing like top tier.
She fills a niche, in that she has easy access to mana on a bad board through her A1, and can fetch a creature with her A2, which can often help fulfill objectives. She’s still pretty great at getting a Ghalta stack out there. And she has access to all the good blue things.
But both Sarkhan and Teferi are basically better at what she does than she is. Sarkhan can go get you three creatures and fill up their mana, and Teferi can get you a fresh hand and two turns of big mana ramping. Plus each gives you access to another color and loses very little in mana gains compared to Kiora. It’s only on events where you’re locking those two to other nodes that Kiora starts to enter consideration.
You mean Tamiyo, not Teferi, I presume.
Kiora wss queen for a long time, though. Her and Koth’s mana gains were tough, “back in the day”. I can still win with her, though. The card access DOES make a big difference, of course…