Perhaps something like
$the_post_type = get_post_type( $post->ID );
switch ( $the_post_type ) {
case 'page':
// you'll need something else to distinguish "landing" pages from normal ones
// which would allow you to then set a flag for it
if ( $some_condition ) $landing_page = true;
if ( $landing_page) {
// display your title with the class that'll centre it
}
break;
case 'post':
case default:
// display your title with the normal class
}