PHP is much much more widely used?
PHP runs natively, while Mason runs on top of Perl?
You could probably port Mason to run in PHP, but would you want to try porting PHP to run in Mason?
Sounds like a category error to try comparing them: Mason appears to be more of an app, while PHP is more of a language. Maybe Mason vs Smarty or FastTemplate or summat like that would be a more useful comparison.
Just a couple of first-approximation observations, given that I never heard of Mason before this post.
