I don't think there is such a thing as a better choice, it all comes down to your intended usage.
PhpNuke is very simple to use but I believe it can be a little limiting. Drupal on the other hand is very feature rich, but can be a little daunting to get to grips with.
There are many more choices for you to ponder over. You might watch to have a look through www.opensourcecms.com where you will be able to test drive various cms apps and portal scripts without having to install them at your website.