I guess that 'greatest' will always be a matter of opinion or personal taste unless we define what greatest actauly means. Most listened to? Most popular? Most covered by other people? Bst known? I think by any of these standards the afore mentioned 'First Time' must be in there with a good chance. As it was written by Ewan MacColl I don't think it's pedigree as a folk song can be in any doubt:-)

Cheers

Dave