MathJax is very flexible and its output is certainly high-quality. However, it is difficult to configure and package in my experience, and it's pretty slow.

We used it for a few years at Khan Academy before building KaTeX (https://khan.github.io/KaTeX/) which is around 50x faster to render in our experience, not even counting download size. We ran an A/B test for MathJax vs. KaTeX on the Khan Academy site and people completed measurably more exercises with the latter, even though they look identical. (KaTeX doesn't support everything MathJax does though – we still fall back to MathJax for a small fraction of our content.)