[yiyus]

You are right, I stand corrected. They actually talk about tensile strength in the PRL article:

"It is noted that lonsdaleite exhibits almost identical ideal tensile strength and only slightly larger pure ideal shear strength compared to diamond. The significant enhancement in its indentation strength occurs under biaxial stress loading conditions. The situation in w-BN versus c-BN is similar. All past calculations have shown that diamond exhibits the highest strength under various loading conditions compared to other materials, which was consistent with all available measurements. Here we show for the first time that w-BN and lonsdaleite exhibit higher strength than diamond under indentation."

So, indeed, diamond is still the winner here.