Best way to get IP address?

What is the best method to get the users IP address? I've seen a couple of codes on the Internet to get the users IP address, like these:

PHP Code:
$ipaddress = $_SERVER["REMOTE_ADDR"];
PHP Code:
$ipaddress = getenv('REMOTE_ADDR');
PHP Code:
$ipaddress = @$REMOTE_ADDR;
and even this

PHP Code:
function getRealIpAddr()
{
if (!empty($_SERVER['HTTP_CLIENT_IP'])) //check ip from share internet
{
$ip=$_SERVER['HTTP_CLIENT_IP'];
}
elseif (!empty($_SERVER['HTTP_X_FORWARDED_FOR'])) //to check ip is pass from proxy
{
$ip=$_SERVER['HTTP_X_FORWARDED_FOR'];
}
else
{
$ip=$_SERVER['REMOTE_ADDR'];
}
return $ip;
}