IBM Model M, when you have to type every blasted character in ASCII7, accept no substitutes.
I'm a bit of a buckling spring elitist... as in for me even the Unicomps feel like soft, mushy, pathetic imitations of a REAL pre-lexmark Model M. The Unicomp offerings seem to be based on the last/later models and because of that they are not as robust in spring strength or build as the pre 1992 versions, and certainly don't seem to "break" as crisply on each keypress.
My own "perfect" M on my workstation is a mix of the 1992 Lexmark keycaps which I like for the larger text on them, the 1984 mechanicals as they are the "true M" feel, and the logic board and outer case off a 1988 model as it requires less electricity than earlier ones (making it more compatible with USB converters), features the detachable cable, and the casing was pristine.
But I'm a bit like Al Bundy was about toilets when it comes to the Model M.
Bud, keyboards today aren't worthy of the name. They come in designer colours and they're too low... and when you type on 'em, you get this little weak, almost apologetic sound. Not the Model M; they only come in beige, and when you type on 'em? Ker-CLICK! That's a man's click Bud. A Model M says "I'm a keyboard, gimme your best shot!" Oh if only a Model M could speak the stories it could tell...
For those who don't know the reference: