My
personal opinion is that hooks should
not be mounted on the bucket
corners because if you are pulling with only one hook you can bend/tweak your loader out of square so that your loader arms are not parallel.

Once that happens the loader arms will never be bent back into square. This is probably more likely to happen on a smaller tractor (anything smaller than ~45hp)
I prefer to mount grab hooks in line with the loader arms. You can still tweak your loader out of square, but the chances are lower because you are not able to put as much lateral/twisting forces on the arm if the hook are in-line with the loader arm verses being mounted all the way out onto the bucket corners.
FWIW, I also bought the weld on hooks from AW Direct.