Currently a friend of mine and myself are working on a site together. We have our login system down, but are using sessions. I, myself, have always used cookies for logins, though my friend prefers sessions. I keep telling him we should have two or more sessions we can compare with the database to make sure it's the accurate user, and not someone who somehow scammed the ID.
For example:
$_SESSION['id'] = $YourId;
$_SESSION['salt'] = $SomethingElseTheDatabaseHas;
This making it more secure instead of just one session that the database can compare with.