The best small bookshelf speaker you ever heard?

Tidal Amea (still awaiting an opportunity to hear the Amea Diacera which is mor than likely even better).
http://www.tidal-audio.de/english/amea1.htm

In the very compact category (12x6x9), Kiso HB1 by guitar and violin builder Takamine leaps to my mind.
http://www.kisoacoustic.com/introduction.html

Always provided, of course, one does not actually put any of these gems on bookshelves, which probably goes for all or most of the previously mentioned as well!

For me, small speakers are a "pick your poison" proposition.

If you want octave to octave balance (my #1 priority), you have to sacrifice bandwidth at both ends or accuracy (or both). A little mid-bass hump, while inaccurate, restores balance. IME, if you want real accuracy through an extended top end, the speakers will cry out for a sub.

That said, the (original) Red Rose Ribbon monitor (ribbon extends above the front baffle), while somewhat colored, is really satisfying as a stand alone monitor. The old Sonus Faber Minuetto is another speaker that made a similar trade-off. I own, and still use both.

Marty

ProAc Tablette's, original model. These things 'sing'. Have two pair which I've used for over twenty five years. They are still going strong. I use them on lead filled Chicago stands. I also have other ProAc units and some Roy Allison units. And yes, you will need a sub to get the bottom, but that is a small price to pay. Of course you need a small room, but that is part of their joy.

Spica TC-50

How about the Platinum Audio Solo? Real bass, great detail, first-class finish.