In a previous work, the authors have presented a comprehensive procedure for the direct characterization of single piezoelectric ceramic fibers in terms of butterfly and polarization loops and blocking force. The ability to investigate single fibers is relevant for optimizing their manufacturing processes, for quality control purposes, and for modeling the response of components and structures. In this study the novel testing procedure is used to characterize commercially available fibers distributed by Advanced Cerametrics Inc., CeraNova Corp., and Smart Material Corp., respectively, and to compare their performance with fibers developed at Empa. Their porosity, grain size and phase composition were investigated to correlate the ferroelectric properties with the microstructure. Fibers supplied by Smart Material Corp. exhibited the best ferroelectric performance, in particular the highest saturation and remnant polarization, the lowest coercive field and the highest P-E loop squareness. The said properties result from a low porosity, a sufficiently large grain size and a phase composition near the morphotropic phase boundary. After removing a surface layer dominated by a rhombohedral phase, Empa fibers developed maximum average free-strains 15% larger than any commercially available fiber. Better control of the sintering atmosphere thus promises to be the key to very high performance fibers.