When I was planning my site, one of many problems I had, was insertion of mathematical equations in my articles, but I found very soon in MathJax a useful solution. Some time after I discovered another method: MathML, even a recommendation of the W3C math working group! Here there are some personal considerations on them: about usability and convenience in my Drupal experience.
MathJax^
I like LaTeX and when I discovered MathJax, a crossbrowser JavaScript library released as opensource, that displays mathematical equations in web browsers, using LaTeX math, I was nicely surprised. Besides it exists the homonym module in Drupal.
Drupal configuration
Once installed and activated the module (see below), you can configure it pointing your browser here: http://my_site/admin/config/content/mathjax. There are few choices in this menu as you can see in the next screen.
In my opinion it should allow the user to enable/disable more easily. I have tried to enable MathJax by a boolean field in Content type but doesn't work! So if I must display equations in a particular content node, I add it in the MathJax configuration menu.
Summary sheet on MathJax
 Here home page of the project;
 here Drupal's module ;
 here browser's compatibility list.
 Pros:
 if you know LaTeX you can use it immediately, for inline maths it is
sufficient insert the equations inside $ \$...\$ $ and for display
maths
\[ ... \]
;  the quality is very good.
 if you know LaTeX you can use it immediately, for inline maths it is
sufficient insert the equations inside $ \$...\$ $ and for display
maths
 Cons:
 you have to install an extra module that load a JavaScript library;
 you have to choose where enable it (all pages or selected pages);
 I suggest you to test your formulas in a good LaTeX editor, above all if you don't use LaTeX every day (like me!);
 make attention when you insert the $ \$ $ charset, because enable it
in your articles. In order to avoid this, use these charsets:
$ \$ $
MathML^
While I was testing editor WYSIWYG Amaya, I have found in its menus some simple items to insert mathematic equations in html page, using MaThML. This is an application of XML for describing mathematical notations and capturing both its structure and content. It aims at integrating mathematical formulae into World Wide Web pages and other documents[1]. I have published only one article with MathML till now, but I don't like it!
Summary sheet on MathML
 Here home page of the project;
 here browser's compatibility list
 Pros:
 it is a recommendation of the W3C math working group;
 MathML deals not only with the presentation but also the meaning of formula components (the latter part of MathML is known as “Content MathML”)[1].
 Cons:
 you need a good editor to type your formulas in this language, because it doesn't appear easy and immediate to learn;
 in Drupal you have to choice PHP Code in text format, because the WYSIWYG, in my case TinyMCE, doesn't interpret it;
 some graphical errors and pagination.
Comparison using an example^
MathJax  MathML 
\[ 
<math xmlns="http://www.w3.org/1998/Math/MathML">

\[ w = \sqrt{{4 \cdot (\gamma_p  \gamma_w) \cdot D} \over {3 \cdot \rho_w \cdot C_D}} \]  $w=\sqrt{\frac{4\u2022({\gamma}_{p}{\gamma}_{w})\u2022D}{3\u2022{\rho}_{w}\u2022{C}_{D}}}$ 
References^
 [1] MathML on Wikipedia
Comments
The title is misleading: You
The title is misleading: You can't really copmpare mathjax to mathml as they are not comparable..At its core MathJax is based on MathML but it has three different input parsers, one of a latexlike syntax (that you were using) one for mathml synatx and one for asciimath syntax. Whichever syntax you used it is parsed into an internal mathml representation. then this representation is rendered by one of three output methids, depending on the mathjax configuration. It can use a html/css positioning, use the native mathml capability of teh browser or use the svg rendering of the browser.So comparing "mathjax" to "mathml" is like comparing "firefox" to "html". One is an implemetation, one os a language.
You're right, I put a forced
You're right, I put a forced title that confuses about the content of article itself. But I have tried MathML because it is a direct language, without any external library to parse my formulas again. Maybe I should fix the title with a more suitable "MathJax and MathML in my Drupal experience", like I explain more correctly in the preamble and in the rest of the article. Thank you for suggestion.