Since we're on the subject:
I have a PSOne controller right here and a Sixaxis. The sixaxis, even though it's half broken, has no issues with diagonals on the d-pad. Feels a little mushier (and more comfortable since it doesn't need much pressing), though cheaper somehow.
The one on the PSOne gamepad which I bought refurbished is weird as fuck. Seems sturdier and brand new, the sticks work nicely and all but the d-pad is just not there. I have to press quite harder for the diagonals and going up -> up-right or up-left for instance is much more difficult.
Any ideas there? Think it's because of the board? Its membrane? I just hate it how it does look like an amazing gamepad, all new and sturdy but at the same time it feels like I have to mash the buttons hard.