I don't know much about game sizes and coding, but Gold and Silver have better visuals, 100 more Pokémon, 100 more moves, more items, quite a bit more beefy sprites, a 24/7 real-time system with a crap ton of events and variables, twice as many music tracks... and much more. That alone should at least take quite a chunk from the extra MB Gold and Silver had over Red and Blue. But then they just went and add  Kanto. I don't think fitting all of that with just twice the memory was an easy feat.

The OG Red/Green were stored in 500KB cartridges, so it's more like 4x the storage, really. Red/Blue were 1MB because by 1998 that had become standard already, not that they were actually using it.

If you want an actual impressive compression feat, that would be RE2 on the N64. ~400-500 MB of data crammed into a 64MB cartridge.

A bit unfair to compare Red/Green with international Gold/Silver. Japanese G/S were 1 MB cartridges, not 2.

On Wii, Shinen, Nintendo, Capcom and High Voltage all pushed it hard.

On Switch, I'd give it to Retro Studios and Next Level Games.

I'd also throw is RE Darkside Chronicles and Monster Hunter Tri for Capcom, two of the best looking games on Wii.

Yeah it's hard to overstate just how insane DKC looked on a CRT back in 1994, it was like if the best looking game on the market came out this year on Switch 2.

It's usually, though not always, Nintendo themselves. SNES had of course the Super FX games. N64, it's a bit of a toss up. Nintendo did some really, really impressive stuff but so did third parties with games like Doom 64 and of course there was Rare. GameCube, Nintendo again. Metroid Prime 1 and 2, Wave Race. There were contenders, sure, like Capcom and Factor 5, but I would still give it to Nintendo and Nintendo's direct partners. Wii, Nintendo, easy. Skyward Sword and Xenoblade really flexed the muscles of the system. Wii U...I mean, it's kinda Nintendo by default. Xenoblade X and Breath of the Wild were super impressive. Switch, probably Nintendo. You have Prime 4, Xenoblade 3, Tears of the Kingdom, among others. Switch 2 so far is third parties though. Resident Evil Requiem, Indiana Jones and the Great Circle, Star Wars Outlaws, and Assassin's Creed Shadows are big standouts.

Handhelds it was usually Nintendo throughout.

Gamecube is actually one I'd give to the thirds.

Don't get me wrong, the likes of Luigi's Mansion, Metroid Prime 1/2, etc looked good, but for me the best looking Cube titles were stuff like the Rogue Squadron titles and RE4.

Nintendo as they'd have multiple titles doing it on their platforms, second place is Capcom as often the next best group of titles pushing the hardware is a Capcom game, third place is where it gets very random tbh.

It might be Nintendo, but it depends on the platform. A lot of Nintendo-published titles (and a lot developed by their own studios) look gorgeous on Switch despite the resolution and processing limitations. Not to mention the impressively low file sizes.
Luigi's Mansion 3 benefits from its cartoony style and enclosed environments. It looks like a CGI movie while running on a Tegra X1 and about 3.2 GB of RAM (not all of Switch's 4 GB RAM is of course available for games). I want it to get a Switch 2 version or free update by now to look even better.

Yeah LM3 still looks crazy good, I can't wait to see what Next Level Games can pull off with LM4 on Switch 2 given the jump in power.