Not sure about reliability, but PS2 Slim sure was tiny!

I have mine sitting in an AV cabinet, a top loader doesn't work for me. Nor placing consoles vertical as it's always guess work which way the label goes lol.

No PS2 model is very reliable.

I actually really like the aesthetic of the Wii Mini, it has an appealing retro vibe. It's just a shame it cut so many things, if it was fully featured it'd by one of my favourites.

A textbook example of form (and stripped to be a budget model) coming at the massive loss of function. I like the look of Wii Mini as well, but it's nothing other than a collector's piece with how barebones it is.

Wii Mini isn't even that expensive secondhand right now despite being uncommon (I believe it sold a few hundred thousand units, there's virtually no chance it hit 1 million units). That shows that the market doesn't care enough about it secondhand as a collector's item (for now). They'd rather play Wii games on the earlier 2 Wii models or on Wii U. 

A piece of hardware I didn't mention in my best and worst was the Top Loader NES/New Famicom. It sits in the middle for me at least compared to the NES. It has a better controller (which you can use with the frontloader) and toploading but is RF only. The lack of standard AV outputs is a massive drawback. 

I remember seeing that thing for like 150 bucks CAD about 12 years ago. Big regret not buying it.

Great Revisions

• GBA SP - Nearly perfect, fixing and tweaking many things without sacrficing quality or increasing cost significantly. You got lighting, a better form factor, rechargable batteries, better battery life, etc. It could do everything you could reasonably want for $99 in 2003... except tell you the time.

Good Revisions

• DS Lite - Anything that manages to be smaller/lighter and cheaper without compromising features is a win in my book. This was the DS model people bought by the tens of millions for a reason. The only problem is that the GBA cartridge slot is a bit too small to keep GBA games from sticking out,
• Game Boy Pocket - Lighter, better battery life, tehnically larger screen... all that was missing was some form of lighting.
• New Style NES - Was a reasonable $50 for a much sleeker piece of hardware. This wouldn't have helped much if the NES was dead by 1993, but even in 1993, you got games like Kirby's Adventure, Bomberman 2, Ducktales 2, and Mighty Final Fight.

Middling Revisions

• Nintendo 2DS - On the bright side, it was a significantly cheaper model that only sacrificed a largely underused feature, while being nice and durable. On the other hand, it's ugly and has worse sound quality.
• Nintendo DSi - Though it had better specs and features like the new DSiWare store, missing the GBA slot was a major blow. Not only did hat entire library of 1500 or so GBA games get locked off, you also were unable to play games requiring certain peripherals, most notably stuff like Guitar Hero and the games that used the Rumble Pack. And the cameras weren't worth the trouble.
• PlayStation 2 Slim - Significantly smaller and quieter than the original, but they cut the expansion bay. That isn't a major dealbreaker unless you wanted to play Final Fantasy XI, but some other games benefitted from it and removing features is always a downer.
• Wii 2011 Redesign - The so-called "Family" model, this sacrificed GameCube controller compatibility for a $50 price drop. I'm tempted to rate it lower, but a $50 price drop is considerable, especially since these thingsusually came with multiple games.

Bad Revisions

• Genesis 3 - Incompatible with hose infamous add-ons the Genesis is known for and even some games that don't require peripherals, such as the Virtua Racing port. Even in 1998, this was arguably not worth the $50 budget price tag; the PlayStation and N64 were already down to $129.99, and although I can't find info on the SNES in 1998, the redesigned "New" SNES cost $99 in 1997 and came with the fairly recent Yoshi's Island
• PSP Go - More expensive, no compatibility with UMD's, a smaller screen, and honestly not that much storage space considering the all-digital design.
• Wii Mini - It's small and cheap, but comes at the cost of many of the Wii's basic features (480p video, SD Card compatibility, ONLINE PLAY, etc). All of this made it sell for $99 instead of $129.

There are loads more, but I don't want to share completely uninformed opinions.

My favorite revisions:

DS Lite
GBA SP
Switch OLED

Worst revisions:
Genesis-3, which was made by Majesco, not Sega
PSP Go
Any PS3 model other than the CECHA series. The PS3 seemed to get worse with every revision.

Yeah the PSP Go was a bloody stupid idea, sacrificing physical media entirely.

2DS sucked as well; I'm not opposed to cutting out 3D to reduce costs, but getting rid of the clamshell form factor and making it a slanted slab instead was a misstep.

The 360 Slim was a winner, in that it solved the system's biggest problem while (reliability) while being visually decent.

While I'm not a fan of the system as a whole the Xbox One S was a visual upgrade over the base model, and even snuck in some minor performance improvements, so it deserves a shoutout.

Always felt like Xbox One S and X were ugly. Just looked like a phat PS2 which was hideous. Bland and boring to boot. Better than OG XBO yeah but it just went from trash heap to reg cardboard box in terms of "improvement"