The split that matters
Macs sold before late 2020 use Intel processors. Macs since then use Apple's own M-series chips. On the used market the two behave like different products at similar prices.
Apple silicon Macs run cooler and quieter, get noticeably longer battery life, and are supported by newer macOS releases for longer. That last point is the one people underestimate: a Mac stops being a good buy when it stops receiving updates.
What Intel Macs are still good for
They are cheap, and they are the only Macs that can run Windows natively through Boot Camp. If you need x86 Windows on Mac hardware, an Intel machine is the option.
They are also fine for browsing, documents and video, which is most of what most laptops do.
The memory decision is permanent
On Apple silicon, memory is part of the chip package. It cannot be upgraded later, by you or by anyone else.
That makes the configuration you buy the configuration you keep. Buying a little more memory than you need today is the one upgrade you cannot defer, and it is the main reason to compare listings on specification rather than on year.
Practical checks for a used Mac
- Cycle count and battery condition, from System Settings or system_profiler.
- Storage size, since it is also fixed on most recent models.
- Whether the Mac is still receiving macOS updates.
- That Find My is off and the Mac is not activation locked.