Here (The Royal Society of Chemistry) You can find such information: densities.jpg .

This document gives the last value as 6.09.

http://media.rsc.org/zinc%20and%20zirconia/zirconia.pdf

As you perhaps realized from the link the density is given by a range between. This is one "problem" that e.g. cubic zirconia is instable and required some doping which then also change the density slightly. Also the lattice parameters are varying which changes the volume and therefore the density as well. Always slightly of course but it sounds from your question ( ..."recently reported values..." ) that you want have the "best". However, new data do not automatically mean the best. "Best" is more a question of what you actually want do with them. And perhaps other values or parameters are more important and of higher impact than the density. Could you tell us, for what do you need the density?

Now I found

Mulaudzi, Masilu Godfrey. "AB INITIO STUDY OF STRUCTURAL STABILITY AND ELECTRONIC PROPERTIES OF ZrO2-xSx FOR 0 ≤ x ≤ 2" PhD diss., UNIVERSITY OF LIMPOPO, 2015.

http://196.21.218.27/handle/10386/1393

Stated in page 3 a table that include these densities (5.68, 6.10, 6.27 for m,t,c Zirconia)

I think these values are based on crystallographic data

Antoniac, Iulian Vasile, ed. Handbook of Bioceramics and Biocomposites. Springer, 2015.

Chapter 4: Bioinert Ceramics: Zirconia and Alumina, table 4. stated that the theoretical densities for m,t,c Zirconia are 5.83, 6.1, and 6.06 respectively. I think these are better numbers.

Here (The Royal Society of Chemistry) You can find such information: densities.jpg .

This document gives the last value as 6.09.

http://media.rsc.org/zinc%20and%20zirconia/zirconia.pdf