I've pondered long and hard on this issue and I've finally decided which grid system Battle Mechanica will use: square grid. Despite the flexibility of the hex grid, I found that the square grid was far simpler to incorporate into the game. Simplicity of design won over simulation of realism.
So why Square Grid? Well, the reason why I chose to use hex grid in the first place was because it models diagonal movements nicely. But I found that hex grid doesn't work well on rectangular boards, since it's difficult to make all the hexes on the edges equidistant with their opposite counterparts. That was the only real issue for me.
Square grid solves this problem, and a whole lot more than I care to admit. It may not model diagonal movements well but it is simpler to implement and easier explain to would-be players.
Battle Mechanicum by Daniel Marcus is licensed under a Creative Commons Attribution-Share Alike 3.0 Unported License.