jointhefediverse.net seems to be a commonly linked resource for directing people to join the Fediverse.
Curiously, it does not list Lemmy under the list of Reddit alternatives. Their GitHub README explains why.
Previous relevant discussion: https://lemmy.ml/post/78808
On what basis can anyone declare one instance to be the ‘main’ one? I’ve seen a number of people claim the same thing about .world, but none of them need to be considered the ‘main’ ones. The entire motivation for the creation of the fediverse is to allow segmentation… I think people simply want to make it an issue because without these little cross-community spats things get boring.