It will depend on your primary purpose and audience.
MathML (MathML2) sounds like promising but it still have a lot of compatibility issues across browsers and MathML equation editors (or generator). Many complex equations will not be maintained or displayed same across different browsers. Many math editors, converters, generators say they support MathML. But the result is not the same although the output may look similar. And it is not easy/not possible to define many complex equations in MathML 2.
If you just have some simple equations and if you can have your audience use a certain browsers, then this might be an option.
If MathML3 is widely supported, then MathML might be the way to go.
If your math expressions are not interactive and don't have to be dynamically generated) and rather static on the page, PNG or JPG image might be a good option. The size of images are not that big in most cases and displaying tens of equations in a page is quite fast as most of us have high speed internet these days. Not much difference between PNG images vs. any script based rendering approaches as the script based equations are often a few KBs and as it takes time to render the images from the local computer after downloading all the scripts.
also, there are many applications that support re-editing of the PNG or JPG based equation images.
MathMagic (www.mathmagic.com) supports re-editable PNG (transparent PNG as well), GIF, JPG, BMP.
MathType (www.dessci.com) supports re-editable GIF. MathMagic also reads MathType images.
If a vector based image format is required for both screen and high quality output such as printing, SVG might be the way to go. Also, PDF can be an option in some cases.
Many Mac equation editors supports PDF format as it is a kind of (almost native) Mac OS X format. But only a few supports PDF on Windows.
It looks the latest MathType Mac version supports PDF. MathMagic supports PDF on both Mac and Win. It looks MathMagic supports SVG as well.
If the equations are created by some limited writers, there are many options to combine to get the best results. Such as using the latest MS Word's built-in MathML/XML based equation editor, and then converting the pages to web. Or using a few 3rd party WYSIWYG equation editors (such as MathType or MathMagic) for fast writing and editing, and then saving the equations a MathML, LaTeX, or Wiki compliant equation format and using in with online equation rendering engines such as codecogs.com or MathJax.
If the contents should also be used for other formats, such as eBook/ePub, there should be other factors to consider including the quality of equations and the integration with the solution such as InDesign.
please correct me if anything incorrect.
