Here are some of my own reasons for using it:
- Security: Because of a thorough audit, OpenBSD is known for being one of the most secure operating systems around.
- OpenSSH: Provides secure shell access to Unix, *nix and Windows.
- pf: OpenBSD's own packet filter. It's easy to use, very flexible and keeps the bad guys out.
- Flexible software: By only using the packages and ports that come with OpenBSD, I've been able to install just about everything I needed to get my server up and running.
- Ease of setup: Once you understand the disk partition tool, setup is a breeze.