Depends on what you mean by professional and your needs.

Debian (stable) is rock solid but (because) slow changing, if your application is slow (or not) changing it's probably the better choice, but if you need new things before it's ready for a new version it'll be pain. It's the professional sysad's choice because they'll likely not have to do anything.

Fedora is faster moving (think cutting edge, not bleeding edge (e.g. Arch) as opposed to Debian's blunt safety) so if you're in active development it's likely a better choice. It is also sort of the testing arm for Red Hat Enterprise Linux, which is the quintessential professional Distro, so you'll learn some of that along the way.