Yea I have, and that's exactly why I created this. Finding them without this tool would have been really annoying. Here's a screenshot of the top 12h rooms:
Right now they are pretty diverse. The two most active I recommend starting off in if you're English speaking are #envs_lounge:matrix.org and #anime:matrix.org
This is the one I made https://matrix.to/#/#all-topics:matrix.org before I created the activity tracker and realized there were several others.
The biggest problem I've noticed is that the amount of "Members" is displayed in clients, but so many rooms have a lot of "Members" but no real activity. Which is what this tracker attempts to solve by looking at actual chat messages and timestamps.