For those of you who prefer buying games physically, what do you consider the best physical format for games?

Do you prefer Blu rays, as standard in modern dedicated home consoles? Do you have a soft spot for old school ROM cartridges? (And if so, which system did them best?) 

Is your preference something more unusual and esoteric? And why is it your preference?

I just collect for the systems I own.

Whether it's cart of disc is pretty irrelevant to that end.

Something to be said about discs having the spine facing outwards without any modification that makes it more manageable to curate though.

Cartridges and cards just feel more real to me, for lack of a better word. There’s a solidness and sturdiness to them. My favorite are N64 game paks. I love the chunkiness, the curved edges, the shiny screws on the back side, the deep lines framing the cover art, and the all the variant colors — blue, green, red, yellow, black, and gold. The only problem is that they’re next to impossible to organize/identify unless the front sticker is facing outward.

I don’t mind whether the game is stored on disk or cartridge, but I do appreciate the packaging of a good collector’s edition. Some of them are really well put together.

Discs always felt the right media to me. If my music albums and movies came in discs, why shouldn't the my games come in discs too ?

Blu-ray. While likely not an issue until decades from now, Switch and Switch 2 Game Cards might degrade over the decades if not used and might even if they are used.
Blu-ray/UHD Blu-ray is cheaper and less fragile.
But if cost was no factor and the Game Cards were a little more durable, I'd prefer them.

I have experience only with systems that use optical media, so I'm not qualified to speak of systems with cartridges or other non-optical media (I guess I could be qualified if I had more knowledge, but I don't). For optical media, Blu-ray has a strong tendency to require game installs, so I'd be tempted to say BD has insufficient read speeds for most games. DVD also had similar issues with read speeds, although I don't recall it being a huge issue in most of the games I've played. On the other hand, I don't recall it being an issue at all in any of the CD games I've played, so I'll have to go with CD. In reality I suspect it's a close call between CD and DVD though, but based on my own, fairly limited experience, CD takes the win. But of course this is all excluding non-optical media, and I suspect there would be pretty strong arguments that could be made for them.

Cartridges

Cartridges.

Yeah I feel the same way, maybe cos my first gaming systems were the SNES and N64, so that's how I first experienced physical games.

They also have the advantage of near-instant load times, and the ability to add custom chips to enhance games, like the Super FX chip used in Starfox and Yoshi's Island.