Ideally speaking, it shouldn't matter much which instance you pick, but that's one of the biggest miscommunications about how all this stuff works, speaking ideally rather than realistically.
Realistically instance choice matters both regarding technical stuff like how well it handles traffic and social stuff like whether folks are discussing anything that interests you to begin with and whether the instance's moderation style appeals to you. When all of this pans out, the tech should fade into the background, but as we've seen, it's early days yet in that regard.