See the sidebar in !communitypromo@lemmy.ca, where you can find some related communities.

Generally people don’t change instances (the site where you made an account) that much, so there is less discussion comparing them. People usually make an account on one site and then don’t move unless there’s a significant issue, and so people tend to only know what their home instance is like. There are some exceptions and controversies, which you might find posted about in places like !fediverse@lemmy.world

Otherwise if you want to discuss communities or request communities, see !lemmy411@lemmy.ca or !communitypromo@lemmy.ca