I'd say Garko had more charisma, but that's actually why I like Steffen better. I don't really like my "anti-heros" to have charisma. I also am not crazy about a lot of the Garko films I've seen. A few were pretty good but the majority do not come close to my top spaghettis.
Exactly where my views come from. I prefer the silent type, and get tired with talky gunmen fairly quickly. Just comes across to me as less sincere when a killer smiles and talks your ear off.
Killer Kid's in my top 20..