I'll do a top 3 by set end-of-year-list (excluding reprint-only releases)
Rivals of Ixalan
Zacama finally gave Naya a respectable ramp target, and boy is it respectable. This card is great and does it all! RAWR!
TIS is an insane curve topper. The abilities are nicely synergistic, you draw more cards, that you then get to play for cheaper, and the creatures get pumped. Pretty sweet value card, and I know I have multiple players that just can't resist value.
The Deathspitter is kind of an odd duck. I initially added it just to expand the enrage theme, and while it works great in the pinger deck (take an additional 2 each turn!), I found it is also simply excellent in aggressive strategies. It fulfills the power >= cmc requirement you're looking for in an aggro deck, which means it should trade with whatever blocker your opponent has most of the time (at least in the early game), but it also deals some final damage when it does die, meaning you still get some momentum out of it. Pleasantly surprised with this, and I'm happy I tried it out.
Dominaria
Teshar is a great new addition to a select group of white card advantage cards. The stat line is unassuming, but it does peck in for 2 points a turn, while also recurring threat after threat if your opponent doesn't deal with the bird. Now, granted, it's not especially
hard to deal with, but at my power level at least, I've been pleasantly surprised how well this plays!
D'Avenant Trapper is my number two. Historic is just so easy to support in white with all the playable legendaries and white weenies' love for equipment. This is reasonably statted at 3 power for 3 mana, and it lets your team get in. The nice thing is, unlike the usual tapping suspects, your opponent can't predict how many defenders to leave up, because you could have multiple historic cards in hand for a double, or even triple tap. All in all this card supports aggressive strategies in white even better than I hoped for.
My last pick is Rona, which is just a nifty combination of card advantage and reanimation. It targets a reasonably wide array of cards, including such charming targets as
Executioner's Capsule,
Baleful Strix, and
Phyrexian Scriptures. I love that it's a grindy card advantage machine that requires a bit of consideration during the draft and deckbuilding portions of the game, and that doesn't blatantly bury your opponent under card advantage.
Battlebond
This release added no new cards to my cube.
Global Series: Jiang Yanggu & Mu Yanling
This release added no new cards to my cube.
Core Set 2019
White card advantage! GIVE ME MOAR!
The vigilance is surprisingly relevant on this body.
Departed Deckhand is great in the ninja deck, as both a (nearly) unblockable card to return, as well as a way to get those ninjas through in the later game.
Finally, yay, a good Tinker target that doesn't break the game! Not that I run Tinker, but I do run an artifact theme that extends throughout all colors but green, and this has been a very welcome addition.
Commander 2018
Try the number one, it's sweet! Plays better than it looks too!
Varina marriages a nice few themes. I suspect this is even better in other cubes, where lifegain matters and zombies are also supported.
Yuriko is the multicolored ninja I was looking for! Never mind the weird "commander ninjutsu" rider, it's just ninjutsu, and a damn fine one at that.
Guilds of Ravnica
They finally gave us the blue Young Pyromancer in Murmuring Mystic! Great card, another one that plays better than it looks!
Quasiduplicate is a card I currently have high hopes for. I've only seen it in some test games so far, but being able to generate two copies of a powerful card for such a low amount of mana is great.
And my final pick of the year, it's amazing how much convoke does for a more expensive
Banishing Light. It's simply a great feeling to curve out a two drop and a removal spell on turn four and keep attacking.