Personally, I try to stick to instances that will only defederate from others if there are major, serious issues, like illegal content and what not, and that are also not largely defederated by other instances. That way, I get to have a more complete experience of Lemmy / the threadiverse without missing out on major chunks of it. I think it's counterproductive that the majority of instances defederate major, legitimate instances, especially now that the Lemmy software allows each individual user to block entire instances if they wish to. This only serves to weaken the threadiverse as an alternative to other major discussion sites. It's even possible for instances to issue default instance blocks on new accounts if they are worried about the new user experience, removeable by the users themselves if they so wish (like lemmy.zip seems to be doing).

The main instances that I've found so far that seem to follow this "defederation only as a last resort" philosophy are the following:

• lemmy.ml (although this one is a bit risky for this purpose because there is constant lobbying on liberal instances to start blocking it, despite it being the original and reference Lemmy instance)
• lemm.ee (my main instance, appears to have the second fewest defederations of other instances)
• lemmy.zip (they don't defederate from much - third fewest out of this list - but I understand that new accounts have for instance hexbear and lemmygrad automatically blocked, which each individual user can unblock)
• lemmy.sdf.org (they defederate from the fewest instances that I'm aware of - the only defederation they currently have seems to be due to technical issues arising from a dead instance)

If you would like to keep contact with the broader range of Lemmy instances, these are the ones I would look into. You can check which instances any Lemmy site defederates from by visiting /instances and clicking the "Blocked Instances" tab.