You don’t need JavaScript for KaTeX. So I suppose the two options are equally fast.
" <script defer src='https://cdn.jsdelivr.net/npm/katex@0.11.1/dist/katex.min.js' integrity='sha384-y23I5Q6l+B6vatafAwxRu/0oK/79VlbSz7Q9aiSZUvyWYIYsd+qj+o24G5ZU2zJz' crossorigin='anonymous'></script>"