I shot a couple of rolls of K64; I'm sad that I never shot any K25.
That said my real "I wish I had..." are:
- I never printed anything with classic Centennial/Kentmere POP paper, and now nobody makes the stuff.
- I never shot any Agfa Scala (though Adox have brought something similar back)
I bought a darkroom enlarger to use the base + column as a copy stand, and I realised at that point that I would have to do some of my own printing, even just once, or I'd always feel that I'd missed out. Those few prints are among the most significant objects I own. And now I _know_ I will do it again.
Mirrorless is my day-to-day photography experience, though, with all sorts of adapted lens experiments.