What is your favorite reflavor/reskin of officially published RPG material?

Savage world Rifts. The setting is fantastic, the 1st party rules are a mess as the best of times. Savage worlds rules set enrich the rifts world by making it a playable.

Honestly, especially after their team up with Paizo, SWADE has been really, really improving and become my favorite system to reskin things in.

Hell I'm thinking about running a Curse of Strahd campaign in Savage Worlds.
- In the same vein, I was in a Shadowrun campaign that switched over to the Sprawlrunners rules for Savage Worlds (which can be used for either Shadowrun or Cyberpunk). Savage Worlds brought out the dynamic action and calculated hacking scenes that define good cyberpunk fiction without being dragged down by clunky rules.

I really enjoyed the D&D 3rd Edition days, with the popcorn of d20-based games. Star Wars d20, d20 Modern, and the Sword & Sorcery Ravenloft were all great fun. The best part is that it was super easy to get your group to try new things, because the mechanics were all similar, if not exactly the same. People like to hate on D&D, but it's consistently been a great base to start from and inspiration for a multitude of other games.

I don't think I'd call D&D a consistently great base to start from, honestly. For certain settings and genres, yeah, but others are seriously harmed by trying to make it fit a fantasy adventure system. Mysteries and heists are forced to include a lot more gratuitous fight scenes just to balance all playstyles, for example.

Similarly, I worry that using d20 as a one-size-fits-all will reinforce comfort zones than expand them. Why would a person play the Star Wars FFG system (which I prefer) when they can play the Star Wars d20 system instead and not have to learn new rules? And if you're making a new system, then you clearly need to include six core stats, because RPGs have six core stats in them, right?

D&D isn't bad, nor is homebrewing D&D for a new setting. D&D as an assumed foundation of all RPGs can be a serious issue.
Honestly, the "hate on d&d" train really became a thing after WotC bought TSR. Also, I completely agree with you: cross-fluidity of game systems was fun to distro hop, basically, for a change of pace/theme — though the recent boom of innovation is especially exciting! So many new concepts and styles of play, and even reimaginings of timeless classics like Planescape, et al. 🥰
- Hating on D&D is a past time that's as old as D&D. I agree though, the attitude towards the franchise ignores that they are generally making a few good small steps for each corporate, huge step back. It's still my workhorse system while I explore games with deeply different tones and mechanics but I haven't found a want to replace it at my table at all.

I'm pretty hyped the Fate of the Eclipse which is an official port of Eclipse phase in the FATE system, but I haven't played it. There is so many stuff I'd like to play and so few time

I think you meanEclipse Phase: Transhumanity's Fate

If I'm reading your message right, I'd like to mention the infinite ways to flavor the 2014 5e rogue. Firstly the rogue gets no resting based resources so it's effectively always on, secondly despite some flavourful descriptive names like sneak attack and cunning action, it's classic abilities are really just bonus damage, more bonus action mobility and expertise.

This means the rogue is really easy to play as a lot of plain professions. Stick your expertise in medicine and flavour your sneak attack as surgical strikes and you have a surgeon. You can do the same with being a ballet dancer, labourer, merchant, scribe, mechanic, whatever. All you need to do is pick your most relevant expertise.

I am searching for a game with pirates and I am seriously tempted by Sea of Dead Men, a pirate flavor of Blades in the dark.

I've played what was essentially Traveller but with Fate mechanics. You'd think the hard sci-fi ethos of Traveller would not mesh well with the dramatic engine of Fate, but it's all in the narration. And Fate is such a great system to deal with things up close and personal, with high lethality and still loads of fun.

My medium from PF1e uses harrow-themed masks for their spirits, kind of like Majora's Mask.

So whenever he wants to warlock it up and start raising the skeletons from the dead, he throws on the Queen Mother mask and slowly shifts into a regal fomorion as influence builds. Whenever its time for crimes like larceny and extortion, The Crows goes on and he progressively becomes a weird birdman. The Cyclone goes on when its time to throw hands, becoming more like an aerial elemental, etc etc. Twelve masks total makes for a fun and visually dynamic character.

@Elevator7009
My own reskin of WW's Vampire is my favourite.

https://gitlab.com/andonome/ww#structure

(I just tooted my own horn with a toot)