There's no real difference between
Maud and
Maude. It's just a spelling variation, like
Sara and
Sarah.
Maud and
Maude are pronounced the same. I'd guess
Maud is older, because this site says that
Maude is a variation of
Maud, and not the other way around.
I prefer
Maud, that spelling, to
Matilda. Both
Maud and
Matilda are ugly, but
Maud is charming-ugly and
Matilda is just ugly and
Maud is not clunky as
Matilda is.