Should I down-grade to Drupal 6.x? There seems to be much better support! If I'm only looking to throw some easy-to-use modules together for a client and then put the Zen theme on, should I stick to Drupal 6.x? I've noticed in my exploration of Drop-down menus in 7.x that there is very little support for it in the form of modules.
D6 is certainly an option, and will likely retain a sizable installed-base for some time to come.  That said, D7 is where the focus is, now, and will continue to be in the future.

In my experience, the simple/basic/popular modules are already quite well supported in D7; it's the more 'exotic' modules that are not quite there yet.  I've moved my site to D7 with relatively few issues -- D7-specific documentation, or lack of it, can be a challenge.

With regards to drop-down menus, Superfish is provided as a D7 module now -- http://drupal.org/project/superfish.  Works well enough here, and the project seems active.