Create separate sidebars for each page unless all of them are supposed to display the same set of widgets.
I guess you will be managing your sidebar widgets through Appearance Widgets Screen (which displays all registered widgets) so just use register_sidebar() three times or preferably register_sidebars() (set number to 3) within your functions.php file and then you’re ready to put these in your template files:
<?php dynamic_sidebar( 'id-of-your-first-sidebar' ); ?>
<?php dynamic_sidebar( 'id-of-your-second-sidebar' ); ?>
<?php dynamic_sidebar( 'id-of-your-third-sidebar' ); ?>
Hope it helps. I might be wrong but I don’t really see a point in creating one sidebar and using logical operators to modify them.