For the most early-Reddit-like experience, I would recommend Lemmy.

I was kinda interested in checking it out for a while but suffered from a bit of choice paralysis not knowing where to start, but since most of them are federated, you see content from a bunch of instances at once, so that removes a bit of the risk.

I ended up creating an account on lemmy.world which is (afaik) the largest instance by user count. Beehaw is (afaik) the second largest, and it has more of a "safety"/highly moderated approach - which is one of the reasons I wanted to distance myself from Reddit, so I crossed that one off my list.

This map was posted on HN if you want to examine the relative sizes of the instances and see the lay of the land: https://lemmymap.feddit.de/