first of all, let me repeat what i have said before,
a hierarchical note system is one of my most beloved apps, i wouldn't live without one.
but having said that, i'm not sure it matter all that much which one you ultimately decide on.
we will do a review of them at some point,
but basically i would look for simplicity, ease of use, ability to search.
you also have to decide if you want to be able to add pictures and stuff to your database (which i do not use, in fact i prefer just plain text).
some good ones:
keynote (GOOD AND FREE! -> http://www.tranglos....om/free/keynote.html
another thing that i have been experiment with lately,
is to use a help file making app for storing my notes...