

The main reason for Ubuntu against Debian is the packages. For Ubuntu, they’re much newer, and with PPAs (launchpad.net), you can often get more and/or newer packages built by other users. For debian, good luck, you’re stuck with old packages (which is the intent of Debian stable, but not nice as a user, that’s for server)
If you need finer control than recursive
chmod
(see other replies), you can also usefind
to match precisely which files/folders you want and use the-exec
parameter to runchmod
on those