and stats I've read, back up that debian is a very popular (if not most) OS for web server applications
I'd love for you to show those stats, because I could show you stats completely opposite.
Debian may be good, but as far as 'widely used', or 'the most widely used'? I'd have to say not so much. BSD has a better shot at 'most widely used', but that still belongs to the redhat crowd, as evidenced in the poll here.
A breakdown of the options above:
-- Fedora - Unstable, because it is redhat's testing bed . If you're comfortable running a test os on your server, by all means, head there
-- RHEL / CentOS - The same exact thing, released by two different companies at two different cost levels. My own personal choice though,
-- BSD - Too 'security minded', not end user friendly at all, from what I've seen. There needs to be a ballance between security and usability, something that the BSD crowd has completely forgotten about.