We are talking about LaTeX in full, not MathJax
1) Strongly recommended: \documentclass[]{memoir}--very flexible well maintained, can emulate book and article. It allows normalfontsize 14 pt \documentclass[14pt]{memoir} -- note how tests are typed for convenience
2) Strongly recommended: \usepackage{hyperref}--makes better pdf, clickable links (in \label--\ref, \bibitem-\cite, in table of content, index) and also bookmarks
3) Strongly recommended \usepackage{microtype}--better typesetting
4) For graphics (LaTeX drawings) \usepackage{pgf}--the most powerful (another pstricks is also great)
5) For presentations \documentclass{beamer}-- nearest competition powerdot