Honestly there's not one clear answer to this because you're current niche of top 10 videos is already a very general area. Sure you could focus on gaming perhaps, but why limit yourself? The reason top 10 channels tend to get so much attention is because either they have a lot of personality and stand out because of this (like Matt Santoro), or they cover every topic, genre, and search result possible so wherever you look, they're there (Like WatchMojo).
With what to do it on, you just got to go with what's hot currently. The gaming industry may be a good option for this because new games are always being made and the fans are always in anticipation of the next game in series, but then again it's the same with movies.
Just imo, I think top 10 is a niche itself and you shouldn't really restrict yourself to one genre if you're doing top 10 videos. If I had to pick only a few, I'd say general knowledge, gaming, and movies/film would be the profitable areas to be covering.
Hope that maybe helps even somewhat,
- Joel