Which is the strongest base?
Looks like it's neither of the three; ortho-diethynylbenzene dianion has the highest calculated proton affinity.  

From Wikipedia


  


according to calculations, ortho-diethynylbenzene dianion is the strongest base, with a proton affinity of $\pu{1843 kJ \cdot mol^{−1}}$.  

This base claimed the title of the strongest base 2016 ish, another base may have grabbed the spot but I haven't been able to find it.

B L J Poad et al, Chem. Sci., 2016, DOI: 10.1039/c6sc01726f