My experience has been that the “Hot” view is most similar to Reddit if you’re looking for new content. You can read about the different sorting here: https://join-lemmy.org/docs/en/users/03-votes-and-ranking.html
What I’ve noticed about the “Active” sort is that older posts that are still getting upvotes and have new comments can remain at/near the top of the list for several days. I think this is good if you want to see where ongoing discussions are happening. On Reddit, I often felt that an interesting post fell off my view very quickly. I know I wasn’t the only one, which is probably why people would post a “remind me” post or “following” post on Reddit so they could come back to it later. Regardless, someone might entirely miss a post that blows up in a community but sees it in the “Active” view and check it out. I like “Hot” because I can see what’s trending up, but I frequently switch between Hot and Active. I’ve noticed that many of the “hot” posts don’t have any comments.
I agree with you regarding quieter communities. Reddit had something in its sauce that allowed posts from less active communities to show up in my feed through all the noise of busier communities. This didn’t happen for all the subreddits that I joined, but rather, the ones I showed an interest in. The downside of that kind of algorithm is it reinforces the echo chamber effect as the algorithm is learning what I like and then showing me more of what I like to get me to stick around longer. This system isn’t (currently) prone to that kind of manipulation.
When I tried that all I get are the comments from all the posts. I’m using the Mastodon website, so maybe it’s your app. Are you see all comments in your feed or just the posts?