Being able to vote for only one keyboard, I chose the RF 87u 55g. I have this keyboard in black, and I have put a set of blue caps on the alpha, number, and arrow keys. All the others including the spacebar are black. The keyboard looks, sounds, and feels great.
I also have a HHKB Pro 2 (black, with white alpha keys and black mods). I love the 60% form factor and great layout of the HHKB, but I prefer the sound and feel of the RF 87u 55g. Both the RF and HHKB have great dye-sub PBT keycaps.
I have also tried the RF 87u 45g, Leopold FC660C, and CM Novatouch.
The RF 87u 45 was a close second to the RF 87u 55g, but I like the somewhat deeper sound and slightly heavier switch weight of the 55g model.
I like the FC660C sound and feel, but I do not like the stock keycaps or the layout. I also prefer the 60% form factor of the HHKB Pro 2 to the ~65% form factor of the FC660C.
The Novatouch is my least favorite among Topre-switch boards I have tried. It is good being able to put Cherry keycaps on Topre switches, but the switches feel lighter than other 45g ones I have tried, I didn't like the sound or feel of the stabilizers, and there was some excessive play between the plungers and switch housings on some of the switches on the board. I would also prefer to program my own Fn key so that there would not be any dead keys on the board (I can do this with the RF 87u). The lack of DIP switches on the Novatouch limits some intrinsic remapping options. Finally, if I were going with a TKL, it would be nice to have an embedded Num Pad and LEDs for CapsLock and NumLock.
Although I have not yet tried this mod, based on my liking for 55g Topre switches and the form factor and layout of the HHKB Pro 2, I think I would like to try a HHKB Pro 2 with 55g domes transplanted from an RF 87u 55g. I also think I might like to do a dental band or landing pad silencing mod on the HHKB Pro 2 or start with a Type-S HHKB Pro 2.