Realforce : Very nice keyboard, heavy, solid, surdy, , the touch feeling is quite light, the keycap are very nice
HHKB : Less solid keyboard, Layout, i like better the touche feeling, Layout, small size, Layout, detachable cable , did i mention the layout ? ;-)
Unfortunately on the topre keybaord you can't have fun to change keycaps to fancy, original, ugly ones (except topre ones and Cliclack's)
Buy both ;-)