I noticed that the order of quizzes on the frontpage isn't always the same anymore, refresh a couple times and you might see it change, or just notice it in general. It's not every time though so I guess there's an algorithm or something.
I have gotten mixed messages regarding this; some say it's random and others say it's fixed. I thought it was mostly fixed but maybe QM goes and edits it to display more prominent quizzes on the top? I could be wrong.
In the first few minutes, it's sorted by times taken overall.