The "best" nostalgic connection would be mid 1990s to whenever 2000s ISDN where you have end to end PCM on a nailed down circuit switched network.

There are a lot of issues to deal with going 2 wire to 4 wire to some kind of carrier and back again in an all analog network, and once you introduce some kind of hybrid network like PCM carrier and TDM switching any remaining analog links are only a liability.

Modern codecs can pack a lot more quality into less bits and with FEC.. so an HD Voice VoLTE or Opus VoIP call are technically "better" than anything used for baseband voice on circuit switched networks in the past. You could easily recreate circuits with dedicated fiber wavelengths these days and have the best of all worlds.

This is fake nostalgia.

There were a lot of places in the world (and still are many places in the world) where the copper phone lines are anything but crisp and clear - lots of noise and hums and clicks and static. That's the rule more than the exception in some places. Now these intrusions are typically not enough to disrupt a voice call, but they were a major issue using modems and DSL.

a modern call phone call, does actually meet or exceed the quality from a landline. I know because I still had a landline until 2019 - and I have a VoIP one now.