Like Erisan here, I use Fedora. I use it because its at the forefront of Linux security innovations.

 

http://fedoraproject.org/wiki/Security/Features

 

However, I stick to using the the previous release for stability reasons and for support for the proprietary ATI cataylist drivers. For instance: when Fedora 13 is released I'll be upgrading to Fedora 12.

 

If you have an Nvidia card, I'd check out PC-BSD 8 too. The PBI system is much like Windows MSI packages and all the dependencies are self-contained inside the that program's subdirectory within the main "Program" directory, thus there aren't any dependency hassles. It also supports the FreeBSD ports tree in a way that won't mess your installation up.