Samba binaries are available for many platforms, greatly simplifying installation. However, binary releases are often not released for some time after source releases, especially in the case of RPM's. Since samba handles authenticating access to machine resources, it's strongly recommended to install from source to enable you to be current with the latest security fixes.
In addition, samba source installation gives you the option to revert after an upgrade, so that you can continue to use your previous installation if the upgrade does not go well.
The rest of this presentation assumes a source installation, which may be obtained from www.samba.org.