* Close to upstream, for early access to packaged software,
* Security is a primary concern: SELinux by default, Firewall by default, PolicyKit, Exec-Shield, Compile Time Buffer Checks, ELF Data Hardening, Restricted Kernel Memory Access, Stack Smash Protection, Buffer Overflow Detection, Variable Reordering, etc.
* Complete transparency of the distribution (including open sourcing all software they create for their internal processes),
* I prefer PackageKit/yum/rpm,
* They contribute heavily to upstream, as part of their process,
* They drive the development of a lot of the software other distributions use (NetworkManager, D-Bus, PolicyKit, PackageKit, ConsoleKit, HAL, SELinux policy, PulseAudio, etc.).
I mainly use Fedora because their community is targeted at contributors rather than users. I switched to Fedora so I could contribute to their infrastructure team and get to play with all their webapps. In Fedora you can become anything you want. You can play with all of the servers, the build servers, updates, wiki, blogs, planet etc. given you've proven yourself.
I've recently begun contributing packages as well. The processes are a lot more complex than Arch for example, but it's all very documented and sane once you get over the steep learning curve. Packages get through a lot more filters before they get accepted and there's also the "send all patches upstream" mantra which makes Fedora special because we are contributing to other distros as well this way :)
