I’ve been happy with mastodon.world and Lemmy.world has the same admin(s).
I think there are two main schools of thought when choosing an instance:
Smaller more interest based. The advantage here is your local timeline/feed will closer match what you’re into.
Larger general interest. Your feed will be less tailored but you have the advantage of more stability, reliability, and commitment to maintaining the instance.
It’s the typical small fish in a big sea or a big fish in a small sea dichotomy
I didn't pick Lemmygrad.ml because of tankies. I didn't pick Lemmy.ml because it was the biggest server in April last year, and I wanted to avoid the biggest servers (same thing with other fediverse pages). Other servers had dozens of users and almost no content. The server I'm on had like 500 users and a moderate amount of content. And it was located in Finland, Europe (I'm from Spain).
I considered lemmy.ml at first, but it had a message asking people to sign up on a different instance because they were overloaded. I chose lemmy.world because the admins had experience running a decently sized Mastodon server.