I recommend WP QuickLaTeX

I got going with it fast! No hurdles. It was easy to install, and it is easy to use. It offers a global settings page that lets me include all of my \usepackage{} in just one spot. That is great. I do not have to include that in every post anymore. QuickLatex also offers settings for font size, cache, image type and more. I just think that QuickLatex has an edge over “WP Latex” and “Jetpack Beautiful Math” when it comes to settings. Also, Pavel (the author) provides support via e-mail. Very helpful for someone new to Latex.

Ravi.