While I can easily find the binaries for the latest version of subversion (1.6) I can\'t find the binaries for Ubuntu (or Debian).
The download page at tigris.org sugges
You can find a debian package for subversion 1.6 in the experimental repositories from debian at http://packages.debian.org/experimental/subversion.
Having said that you would probably be alright working with version 1.5.4 from the ubuntu repositories, if the svn server you are using isn't running 1.6 you won't be able to use any of the new features in the client anyway.
If I was you I would first try to use the version in the repositories before installing it from a third party as you may find that it does work for you and it will make your life easier when it comes to updating subversion in the long run.