Recommendations on accessing current user data in WordPress

You can use wp_get_current_user() instead of using the $current_user global.

$my_current_user = wp_get_current_user();
if ( $my_current_user->display_name ) {
    echo '<p>Welcome ' . $my_current_user->display_name . '</p>';
}

Note that I used $my_current_user instead of $current_user as a variable name, because you can run into trouble if you use the global variable’s name.