Scratches are more an issue for the finish on top of the wood, which will be identical for all of them. At least for natural colored wood….if it will be stained then scratches could be more of an issue, but it will be an issue for all.

While “strength” can be judged in a variety of ways, in this instance it’s largely about which will show compression/denting the easiest.

All of these woods are good, or else i suspect the company would not offer them. For “hardest” I’d lean to the white oak and pecan…but the differences is marginal for a desk. My recommendation is to buy the one that appeals to you most and will make you smile when you use it.