What do people think is the best "slim" re-release to date?  For that matter, has a list of them ever been compiled?  From my research (please fill in any gaps) I've come up with the following list*:

Mattel Intellivision II (1982)

Atari 2600 Jr. (1986)

Sega Master System II (1990)

Commodore 64 GS (1990) (a gaming-only "slim" version of the C64, which I included here as many people bought the C64 as a game system)

Nintendo NES-101 "top-loader" (1993)

JVC Wondermega/Sega Genesis II/Sega CD II/Sega CDX (1992-4)

Nintendo SNS-101 (SNES 2) (1997)

Sega Genesis 3 (1998) (a third-party release, but done under licence from Sega so I count it)

Sony PSone (2000)

Sony Slimline PS2 (2004)

PS3 Slim (2009)

Xbox 360 S (2010)

PS3 Super Slim (2012)

Wii Mini (2012)

Xbox 360 E (2013)

Xbox One S (2016)

PS4 Slim (2016)

I suppose "best" is relative.  Is best the one that added the most features?  The one that reduced the space and/or mass the most?  The one that was the most attractive?  Let's discuss!  :)

* When a system had different names around the globe, I generally favoured the North American name as it's the single-biggest game console market.  For the year listed, I used it's first release even if it was a limited one (such as the Wii Mini which was only released in Canada in 2012, before a wider release in 2013).

PS2

Either the PS2 Slim for how small and compact is or the Xbox 360 S for how nice it looks.

PS3 Slim

The Xbox 360 E.

PS2 slim, I bought 2 when they cost $99.
That's how you sell a slim.

Xbox One S. it just had a ton of improvements over the base console and that hasnt really been seen in other slim models yet.

a close second is the PS2 slim model. for the size of the original PS2, the slim is a huge cutdown on size. almost to the point where its portable.

Ps2

Dang, this pretty much sums my thoughts as well. I'd say between these 2 slim consoles as well.

   My sense is that the Sega Master System II, the C64 GS, the PS3 Slim, and the Wii Mini are all disqualified because they lost too much.  The Wii Mini was particularly bizarre as it lost a key feature in WiFi (yes, it lost WiFi!) while being only slightly smaller than the original.

Most of the other mini redesigns were smaller, lighter, and cheaper (to make, if not sold cheaper), and might even miss a feature or two from time to time (optical audio in the PS4 Slim, for example), but I believe most consumers would consider them functionality equivalent.

That means, to my mind, there are three with a credible claim to the throne:

Xbox 360 S:  This was a big deal.  It was a little smaller, but it was the model that signalled the end of widespread RROD problems (and anyone who lived through that era knows that was huge).  It also was the first Xbox 360 model to have integrated WiFi, and the first one to go to a 250GB HDD for the deluxe model, and the first to have on-board flash storage for the base model.  The Xbox 360 S was also the first model to not require extra cabling for the Kinect, back in a time when Kinect was promising and popular.  The Xbox 360 Slim was a big, big deal.

Sega CDX (Multi-Mega in Europe):  The Sega CDX was a premium product that few could afford, but that almost makes it more legendary rather than less.  It was a Sega Genesis and Sega CD (or Mega Drive and Mega CD if you prefer), all in one.  It cost more than buying the two separately, but added the ability to take it with you as a portable CD player.  Compared to what it was replacing, I believe this one to be far and away the biggest size reduction of any official "slim" model.

Xbox One S:  This is the only unit that is actually more powerful than the model it replaced.  While it doesn't make a difference in every game, it does boast improved frame rates and less screen tearing in some titles.  The total list of improvements in the Xbox One S is suprisingly long:  HDR colour in supported titles, an IR blaster in the console itself, streaming 4K output, UHD, BD-XL, an improved controller (bluetooth, better shoulder buttons, longer range), support for being placed vertically, moving the power supply inside despite the size reduction, and all of that in addition to the 40% size reduction and the significant reduction in power consumption.

Those are the top three IMO in no particularly order.  You can argue that the Xbox 360 S is the biggest reliability improvement (the build quality of slims are often worse than their original, but this one was better).  You can argue that the Sega CDX was the biggest size reduction.  You can argue that the Xbox One S is the only one to add power and has the most impressive list of added features.  All three have a credible claim to the throne IMO, depending on what you find important in a slim re-release.