I find macOS to be sluggish when it comes to opening apps. But it's not a deterioration, it's just always been like that.

That's my experience on M4 Mac Mini and M3 MacBook Air.

Same, I bought it with the justification that this would be future proofed for 4-5 years. Nearly 5 years later with daily usage, it's not limping along, the battery isn't on its last legs, it's doing great. My impulsive side is annoyed that I don't have a justification to buy the next latest and greatest.

Is it amazing for LLM stuff? No, but that's the same story for anyone else _not_ spending boatloads, or willing to hack on weird mining cards.

I have an M5 pro at work, and certain things are a smidge faster than my personal M1 Max, but they're pretty close overall.

Given how much more you can get buying used versus new, I'd go used unless there's some feature/characteristic only the new hardware has.

Having said that, I could see stuff slowing down over time with OS updates/etc. I've had my M1 air for a while, and some UI stuff was slower after specific updates (I think glass in particular).

Same, although my M1 pro has only 16 GB of RAM and that does seem to slow it down a bit with my current usage. I recently bought a used Mac Studio M2 Max with 64 GB RAM and it's much faster, both subjectively and objectively by looking at how long it takes to run the full test suite of the Rails app I'm working on.

Same. I have an M1 Pro (personal use) and a M3 Max. Whenever I do side projects on my M1 Pro it feels nearly identical.