Someone correct me if I'm wrong but I believe that OpenSSH is just a free version of the SSH protocol. Not sure what alternatives there are to OpenSSH but I think it's pretty much the standard for Linux distros. For more information, check out
http://www.openssh.org/.
FYI: A security vulnerability was recently discovered in versions 2.3.1 to 3.3 so if you have one of those versions, I would update it.