There are too many threads to keep up with on this forum. The only way to have any chance at all is to have multiple lists, arranged in a priority hierarchy.
I use the watchlist. I also use "Show new replies to your posts". The latter has far fewer threads in it, so it's the first one I check. But I also have the problem of having once replied to a thread but no longer having any interest in it.
With the ability to automatically add new threads from specific forums to the watchlist, mine tends to get rather large. I'm no longer able to keep up every thread in my watchlist, so now just browse subject lines to see which threads might be interesting.
I hardly ever make it to "Show unread posts since last visit" any more because that list is even more difficult to keep up with, and that's with most of the forum areas on ignore.