If by "niche" you mean high quality, in depth content that takes effort to digest, as opposed to brain candy that makes you feel like you're in a special club when you're not, and that you're thinking when you're not, then I would very much prefer the "niche".
>> People complain about how HN is getting worse. That's probably true and it is true (and will continue to be true) of any such social site in the future.
Two things:
1. "Worse" is subjective.
2. I think it's more of a trade-off between quality and size. Hacker News doesn't have to get "worse", but would have to remain niche in order to avoid it. That is why subreddits can succeed, because Reddit is essentially a platform for lots of niche communities.