from a European viewpoint I would say:
The Bowie knife, because that is what Zeb Macahan used

and in the early B/W TV years he was the biggest hero there was and every kid wanted a bowie knife. even a Mora knife was a decent substitute when you were seven.
Closely followed by the "Rambo" knife, because that made every young kid drooling over cheap "survival" knives with compass on the handle, sharpening stone on the sheath and the obligatory fish hooks and matches in the handle. You saw them everywhere, they cost nothing and were crap but if you got one you were as strong as Rambo.
Well, MacGyver used the SAK, but that is not a knife from USA, but still.
The Ka-Bar is a part of the North american heritage, so is the barrel knives invented by swedish immigrants in 1900 something. I think though that the Ka-bar has not had that impact outside the US, even though every GI wore one there was no TV series where it played such a significant role as the Bowie and the Rambo knife and by all means the Victorinox. Zeb wouldnt have survived one episode of Bonanza without his knife, in Rambo the whole film revolves around his huge knife and so does MacGyver, his whole existence was dependent on the Victorinox. An early example of product placement maybe?
I know that both the Bowie and the Rambo knives have other names but if you tell someone that you have a Gil Hibben knife at home they go Huh,what?