Are Avids BB7 superior to the Hayes Stroker Ryde? I know one is mechanical (BB7) and the other Hydraulic (Hayes)? but I have both and I need to decide. For a XC use, which would you keep?, and why? PS: I'm upgrading from V-Brakes (Shimano XT group). So these will be my first Disc-Brakes.

As mattnz hinted at in the related question, not all hydraulic brakes are necessarily going to perform better than cable brakes, and it looks like you've hit that nail on the head with this comparison.

The Stroker Rydes are well known to be painfully poor quality. You would have absolutely no reason not to choose the BB7s in this case.