If you are personally trying to archive Reddit. That is really up to you. I can’t tell you what would be important to you. For me i would focus on many of the technical subs. Like r/homeassistant r/jellyfin, r/selfhosted r/homelab etc… They often have technical support issues or setup guides that are very useful and only documented of Reddit.
If you are talking about what should we as a community should focus on I would recommend running and Archive Team Warrior.
The archive team will figure out what they want to download and it will do everything for you. It will eventually get uploaded to archive.org. and require zero space on your part. Only a somewhat good internet connection is required.
Not much currently stands out to me as needing for my personal archive, but I’m sure I’ll miss something when it’s gone. For now, I’m downloading the torrent from Pushshift: https://academictorrents.com/details/7c0645c94321311bb05bd879ddee4d0eba08aaee
Great tip of the Archive Team Warrior btw. I’ll set that up later.