My top three (the order is tenuous, like ordering your favorite children):
(1) The keyboard that stood the test of time for me was the Silicon Graphics model 9500801 and 041-0136-001. These are of the Indigo/Crimson/Onyx line. Original unsimplified white Alps in there; not rubber-dampened; heavy, quiet, very lovely to type on. An under-appreciated classic. Alas, these keyboards have a proprietary interface, which limits their portability. The differences between the two models are (as far as I know) the color: the 9500801 is beige, and the 041-0136-001 is granite. The 9500801 may have different switches, but I doubt it.
(1.5) The original Apple IIgs keyboard (a.k.a. Apple Desktop Bus keyboard A9M0330). While my first interest in computer keyboards stems from coveting anything with actual keys, back when I had a Timex-Sinclair 1000 (membrane hell), this was the first keyboard that made me sit up and really take notice. I list this under (1) because it also has Alps inside, but I never fell in love with the layout.
(2) Model M Mini. I like small keyboards and buckling springs are sweet, and a worthy challenger to the unsimplified white Alps. Nuff said. If Unicomp made a mini form factor BS keyboard in USB, I would buy one just because. Possibly even two, and make them my main boards.
(3) HHKB Pro 2. I just bought a backup, plus extra keycaps to create a custom color scheme. I think it looks pretty sweet. (Photos are forthcoming, post-holiday. I'll also put the remaining keycaps on the marketplace, in case anyone is interested.) The more I use this keyboard, the more I think its function-derived layout is a work of genius. That said, the Topre switches haven't stood the test of time (they make my hands tired), and the "Unix" layout (specifically the remote upper-right location of the "\"/"|" key) can be irritating.
Dream keyboard: HHKB 2 with BS or white Alps and a standard US layout. Another nuisance with the HHKB 2 is the (by default) single Fn key, so if I was designing the HHKB 3, I would probably add a few keys on the bottom row, to fill out the modifier set. And I would make it heavier, with more robust feet, to hold its ground better.