The end grain is the hardest and most durable of all three options. The cut blocks are stacked vertically and flipped 180 degrees so the end grain forms a checkerboard on the top surface of the countertop.
This is the tried, true, and traditional way of making butcher block. The edge grain is a face grain cut into blocks and turned 90 degrees so the cut edge is facing up. Pores are tighter on this axis, and the grain now helps to reinforce the surface