This all started as a meme, we all know that, but really, let's look at this from a different viewpoint for a couple minutes. All of us probably have experiences in both games, so I'm going to respond thinking about someone that may not have played either.
Minecraft is by far the less toxic. It's more user friendly and easier to begin playing when you have little experience.
My first time playing Fortnite led to its uninstallation less than 2 hours later. I didn't like that, although matchmaking was tailored to people of your skill level, it wasn't easy to understand or to get kills. I know that's relative to me, but the game felt like there were too many people.