problem is I have no idea which of these communities is "best"
Its a bit basic but so far I've just gone with the largest population. Usually I'm just after the most activity and that generally scales with population. It keeps things relatively simple.
There is some lemmy.world sure but also:
If a topic suits the philosophy of its lemmy instance its more likely to attract a healthy population. Then when I'm looking for a community on a topic it doesn't really matter which instance that community is on.