It will be the release candidate. If you are upgrading just use the update
manager. Launch it with update-manager -d from Alt+F2. If you are doing a
fresh installation then download the RC and then do the updates to upgrade
packages to be equivalent to the final release. My experience has been that
there are several last minute patches on the Tuesday before the final
release, but the final packages are set. There will be no changes as things
are frozen. RC + patches = final release.

I've been running Lucid since January. It has come a long way and is going
to be worth installing for many reasons.