Your inheritance tree looks like this:
user -> regular -> moderator -> admin -> superadmin
With how ULX works, any member of "admin" is also considered to be a member of "moderator", "regular" and "user". Therefore, the preferred method to select ONLY user and regular groups would be to use the string "!%moderator" (This means, can NOT select any user in group moderator-- which means they can't select admins or superadmins either)
And if I'm remembering correctly, you should be able to let them target themselves by adding ^, so your final string should look like this:
"!%moderator,^" (This means can't target any users that have access to moderator permissions, and they can target themselves)
As for the ignore can_target checkbox, that ignores any restrictions applied to the GROUP as a whole. You can view what that restriction is by clicking on the dropdown box at the top-left corner of the groups tab, and selecting "Manage Groups..." (By default, groups are only allowed to target their own group and any groups below them)