I have a Model M with the flow-thru option; keyboard is probably 30 years old or so.

My mobo still has a PS/2 port, but I bought an adapter for USB when that time comes. Other than needing a really deep cleaning (something I really need to do) - it works flawlessly.

And it doesn't have any of the "Windows Key" junk that happened in the 90s to distract from my *nix aesthetic. Only downside is that it is beige, while the rest of my system is black.

When/if it ever breaks - I have another one waiting in the wings, plus a Unicomp USB classic also available (I've been thinking about swapping it out to keep the aesthetic - and replacing the 'doze keys on it with Tux keycap covers or something like that).

Somewhere, in my junk stash, I also have an old SGI keyboard that I need to look into making an adapter or something for...