If your mother prefers females I would
pick her out a female.
Males do tend to mark whether they are
spayed are not, but so can a dominant female. If your mother has a nice
back yard with plants and bushes that
is a PLUS for a female. Just asked my
sister who will not own a male dog again.
My male as killed all my ground cover with his urin. I have a strong grass so neither
the females nor the male's urin damage it.
Of course if you train him to pee in a certain spot that would take care of it
possibly.
A female will also be smaller and might
be easier for your mom to handle.
Male/Female are both loving and equally
intelligent.
It all comes down to personal preference.