I would avoid lemmy.world, just to spread the risk around.
A mid sized instance like lemmy.ca, lemmy.cafe, sopuli.xyz should work well
And of course, check to see that your prospective new instance isn't de-federated from communities that are important to you, or something else strange, like lemmy.zip allegedly geoblocks UK IP addresses.
Some large instances are defederated from lemmynsfw.com, so if those /c's are important to you...
lemmy.ml is defedded from ani.social, so if any of those /c's are important to you...
Several instances are defedded from hexbear.net, beehaw.org. Again, if you like any /c's on those instances...
And of course, if an instance hosts a lot of groups that are important to you, it might be a good idea to sign up there.