Lemmy user for a couple of days here. I jumped on lemmy.world because it was big and the name suggested it was universal and open, it had open registration and allows nsfw content.
I suffered through the technical issues many of us experienced, but everything seems much better and smoother now (maybe because they were able to fix the issues, or maybe because enough people left because of them, I can't say!)
Does it matter what you use? Yes and no, I guess. Apparently the last few days performance issues were mostly local to dot-world. I did make another profile on lemm.ee and I noticed the different instances seem to show different feeds with some different content, but also many of the same posts from the same communities as well. I'm still trying to figure out how they decide what they show in their feeds. Something to do with federation, I guess, but I'm not pretending to understand the meaning of that concept yet. Given that instances can choose to federated or defederate, it seems like it must matter to some extent what instance you are on even though content can be shared between instances.