Whatever works for you. lemmy.world is the big dog so there's a tonne of activity here but it can be a little slow at times and the target of malicious attacks. You will also find that the front page can be a real fire hose of content.

If you look around you can find regional instances that serve up a more local slant on things or a topic specific instance that looks technology, books, etc. Or you want somewhere more aligned with your politics or an instance with more porn.

There's something for everyone and no one-size-fits-all answer to your question.