I personally use objects, but arrays are more feature rich, e.g. you can merge arrays, enumerate keys, and so on. But since Drupal 7 was announced to require PHP5, I would rather postpone this decision until we know in which direction the core code base will evolve. Either PDO will be available to modules, in which case there's no difference, or maybe (just maybe) another data abstraction layer will be introduced, with node_* hooks being replaced with interface implementations, then it will most likely be objects.
<br><br>-- <br>hex, out.