MBauer et al are needlessly confusing the overall accuracy of the whole recording/playback chain (where we are at the mercy of the guys twiddling the knobs in the studio) with the comparatively simple matter of determining the accuracy of a single component (speaker, amp, whatever). In the case of a single component the "baseline" is simple:
The output signal should match the input signal. This is determined by measurements.
Granted, the speaker/room interface is very complicated with zillions of variables, but even then there is a general consensus on what constitutes an "accurate" speaker: flat on-axis frequency response that is maintained over a fairly wide angle with smooth rolloff beyond that (as measured in anechoic conditions, which removes the room variables), and low distortion. Such speakers will "sound good" to the vast majority of listeners regardless of their audio sophistication, according to the oft-cited work of Toole and Olive.
Still, within that general consensus there is room for preferences even among us "purists", especially in how the speaker interacts with the room: wide (or omnidirectional) dispersion vs. "controlled directivity", monopole vs. bi/dipole, line source vs. point source, and so on. (For the record, I'm a "point-source dipole" guy.)
As to which speaker is best, the answer to that is also simple:
MINE!!
I think b-panther-g nicely describes the two audiophile types, btw.