I would say from experience that the Dragon is harder to play compared to the Najdorf because there are about a handful of forcing lines that go deep and you simply must know.
The Najdorf, black can complicate the game where both sides have counter play.
I wouldn’t lose sleep either way, most times you will get an anti-Sicilians at the club level.
The Najdorf is more flexible and also more positionally sound. In that sense, it has more lines to learn but it's worth it in the long run.
Also I remember Anish Giri saying that in the Najdorf, you don't often have to follow forcing, theoretical lines as much. This is because, in most given positions, many different moves are possible and black can still be doing very well.
The Najdorf and Dragon are both very aggressive, but I think the Dragon is a bit more aggressive.
It's like, in the Dragon, you go all-in and play either to win or lose.
In the Najdorf, you play to win but can still fall back on a decent position if needs be. Some lines are still very crazy though.
As an intermediate/advanced player (1600-1800), being able to face both is important. But trying to play one, which has more success on that level? I'd love to hear differences in how complex and explosive the lines are, how easy either one is to make a mistake in, and overall how each play out in your personal experience