Rex and Nadav, thanks for your comments.
Regarding the chance that the resource types will be hidden "below the fold", I tried upgrading assignments on my site (which I assume admins will quickly do when they upgrade to 2.3) and found that, when using a screensize of 1024x768, all activities and resources were displayed with no scrollbar at all (see attachment).
I agree that teachers generally use resources a lot more than activities, but I think that listing activities first is a way of encouraging / highlighting the use of activities. As the chooser is to be called the 'activity chooser' (not module chooser as stated in the title of this issue), surely it makes sense for activities to be listed first?
I've added Martin as a watcher for his comments.