Personally I would choose Demonstration mode, because it
allows you to have more control over timeline editing. Once you
start recording in Full motion, you are creating a single linear
movie (until you pause or end).
So In both modes you are recording everything. The difference
is in Demo mode you can remove a slide or a background or object
that doesn't fit or doesn't flow. Also you can include full motion
captures in Demo mode, (check out the recording settings), and I
would for any action that requires real time action, like
scrolling, and clicking and dragging.
Hope this helps,
TM