As far as I have heard, the HHKB is the most "Springy" and poppy feeling, the Realforce a very stable and sturdy feeling, and people have said that 45g realforce feels a lot duller and mushy compared to 45g topre in a HHKB, and that 55g feels just right in terms of the realforce. and I haven't heard much on the Novatouch.
The feel is mostly linked to the mounting method. Realforce is plate mounted, and the HHKB is case mounted.