>>116009 (OP)Obviously Azumanga if we define "slice of life" as meaning what most people think of when they think of the term "slice of life", if we use that narrow definition, as "slice of life" in that sense was established by Azumanga and didn't exist prior to it – the authors and studios that made all the "Azumanga-esque" girl-cast animes after Azumanga looked at Azumanga as the recipe/formula to follow and tried to imitate it in various ways. So when people think of "slice of life" most think of Azumanga and its imitations (and a few that don't owe their existence to Azumanga but are somewhat alike such as Aria). That's what the term means, what it encompasses, to most people. Because of that, the term "slice of life" is kind of bad because it's effectively just a mental concept or idea in people's heads to describe "Azumanga-type animes" basically.
A more proper and more real and better term – because it includes but isn't limited to the aforementioned meaning – is "daily life" which is what anidb uses instead of "slice of life". "Slice of life" doesn't exist there, due to the aforementioned problems with that term. "Daily life" encompasses more than what most people think of when they think of "slice of life". Here's a search result for "daily life" sorted by time (oldest anime first, newer ones lower down, click on "Next" to get newer ones):
https://anidb.net/anime/?airdate.start=1900-%3F-%3F&airdate.end=2004-%3F-%3F&atags.include=daily%20life&h=1&lang.dub=2&noalias=1&orderby.airdate=0.1&orderby.name=1.1 – as you can see there are many "daily life" animes very different from Azumanga/SoL, although keep in mind many of those aren't "daily life" focused but feature a "daily life" element which may not at all be the central aspect of the anime (the more stars an anime has next to the word "daily life" - on its page - the more "daily life" it's supposed to be).
If we use the narrow definition of "slice of life" (which is just "Azumanga-type animes" essentially) then obviously Azumanga. If we however don't use that narrow definition, if we use the broader ("daily life") definition, the answer definitely isn't Azumanga (nor anything made in the last 22 years obviously). And it becomes difficult to correctly answer the question of which is the best anime of this sort. It's safe to say none of us have sufficient perspective on this to be able to properly judge which truly is the best, so anyone saying this or that anime is the best "daily life" one – he'd almost certainly be wrong.