Mac OS X is the best *nix OS for the MacBook / MacBook Pro and Mac desktops as well.

DesktopBSD is suitable for the other laptops as it aims at being a stable and powerful operating system for desktop users, combines the stability of FreeBSD, the usability and functionality of KDE and the simplicity of specially developed software to provide a system that's easy to use and install.

DesktopBSD can run on any decent i386-, AMD64- or EM64T-based computer. We recommend at least 6 GB of disk space and 256 MB memory for installation. For more information visit http://www.desktopbsd.net

Ubuntu is also great for Desktop Use and it is a Linux Distro. While talking about Linux Distro's CentOS is also great with enterprise features based on Red Hat.

I presonally use CentOS, Ubuntu, and FreeBSD as Desktop OS in my work place coz they all are stable and relaible.