I've seen people point to specific subreddits as quality before, but I've never found it to be true.

To verify, I just did a quick peruse through /r/AskScience. While the questions themselves are generally good and the SNR is definitely higher than Reddit overall, I hardly think it's an emblem of quality. There are plenty of drive-by comments with low substantive value and the combination of Reddits norms and algorithms don't seem to do a good job of burying those—even on the "best" subreddits.