I started out on an IBM XT keyboard, then moved to a full-size IBM Model M, and now I use an IBM SSK reconfigured to a HHKB Pro 2 layout. Along the way, I tried out a wide variety of form factors (60%, 75%, TKL, and full-size), layouts (ANSI, ISO, and HHKB), switches (Alps, Buckling Spring Capacitive, Buckling Spring Membrane, Cherry --blue, black, brown, clear, green, red, white --, Matias Tactile, Rubber Dome, and Topre 45g), and keyboard makers, including most of the usual suspects (AST, CM, Dell, Ducky, Filco, Fujitsu, HP, IBM, Keycool, Leopold, Tek, and Unicomp).
After all this, two all-time favorites have emerged:
The IBM Model M SSK and the HHKB Pro 2. I really liked the HHKB Pro 2, as you can see in my review:
http://geekhack.org/index.php?topic=48804.0However, more recently, I have been missing the precise feedback that I get from the IBM SSK, and so I went back to the IBM. This initially proved difficult, because I had adapted almost immediately to the highly intuitive and efficient layout of the HHKB. Therefore, I reconfigured the IBM to the HHKB layout, as you can see in this post on DT:
http://deskthority.net/keyboards-f2/ibm-ssk-reconfigured-as-hhkb-via-krm4mb-t7719.htmlI like both, the IBM SSK and the HHKB Pro 2, for different reasons. Now that my IBM has the HHKB layout, I can easily switch between them.
As for Topre, my first experience was with the Leopold FC660C; I liked the feel of this board, but I much prefer the layout and dye-sub PBT keycaps of the HHKB Pro 2. If I were to get another Topre board, I think it would be the 55g RF 87u, although I have not tried this one.