For a puppy I keep it as positive as possible but a light scruff or time out is used if warranted.
As the dog gets older my expectations go higher and I do use a prong if warranted. Never harsh corrections, mostly himself correcting or a jingle on the leash to warn and remind him I mean business.
Any correction that is given should always be done with a clear head and never in anger. Also, the punishment should always match the offence. That's my opinion and while no one is perfect I try to always keep that in mind, GSD are very smart dogs and will give their respect when earned. At least that's what I've found with Delgado
Jasmine - Female Miniature Poodle - born Aug 15, 2010
Loker Delgado Von Stalworth - Male GSD - born Jan 26, 2012
Koda & Zazu - 5 year old male cats
Alex - Male Cocker Spaniel (rescue) - RIP Cuddlebug 2007-2010