64GB (8 x 8GB) OR (4 x 16GB): Which DDR4 kit configuration is better?

A friend is planning on purchasing 64 GB of RAM. Motherboard will have eight RAM slots. CPU will support up to 128 GB of RAM (i7-6800K). I assume that she'll be going with quad channel.

Question: Should she get the 8 x 8GB kit or the 4 x 16GB kit, and why?