Hexagons do have the benefit of being isotropic, however.

They have a higher order of symmetry than rectangles, but how are they isotropic?

I've probably remembered something wrong here, nevertheless the centres of all adjacent hexagons are of equal distance to the centre of the central hexagon. In contrast, a square sharing one vertex (diagonally adjacent) with the central square is farther than the square sharing one edge.

That's only if you use a scaling factor of 9 instead of 4.

edit: Wikipedia tells me hexagonal tiling is conjectured to be the tiling with the smallest perimeter per cell, and is the densest way to arrange circles on a plane. So that's a big plus when binning.

Click through gets you at http://mathworld.wolfram.com/HoneycombConjecture.html, which shows it is not a conjecture anymore. It was proven in 1999-2001 (I do not know whether the ArXiv version needed improvements)