i like the top one better
all layers&way 3 ways i can think of atm
1) ctrl-shift-E, then ctrl-shift-U; merge visible, then mode-adjustments-desaturate;
you will have no seperate layers after that
2) set to greyscalel you will lose layers
3) to keep layers, click on layer, ctrl-shift-u to desaturate
do this for each layer.