Drupal 5 Looks Promising
WordPress and Drupal are the two open source scripts that i am still paying attention to. They are both my favourite and i always need to struggle on which one to use. Bloglah, which is one of my current project, has been switching between WordPress and drupal platform for a few times. Currently, it faces some technical problem again and I have already aimed Drupal 5 as my next target.
Drupal 5 seems to be quite promising to me and its new features can be seen through this video. However, most of the module developers are still waiting for the final version of Drupal 5 before they upgrade their modules, therefore if you thinking for upgrade , you might need to wait for the final release.