I'd have to say the Classic, it's pretty ubiquitous.
I'd have to go with that. As far as SAK's I've actually seen in the wild, I wish I had a dollar for every set of keys that had a classic dangling on them. Yeah, the tinker and champ get the glory, but in the real gritty world of mostly non knife nuts, I've seen the humble little 58's in every color known to man, and a good deal of advertising from pharmaceutical companies to car brands. It's the give away SAK. There's probably more 58mm's floating around on keyring, car glove boxes, desk drawers, and Altoid can survival kits, than any other three SAK's.