I don't really like either, I think they both sound quite comical and cartoon-ish and, at least where I live, would have the potential for teasing. I don't mind
Percy on its own, but
Percival sounds a bit wimpy, and
Ignatius makes me think of the word ignorant. I'd also assume an
Ignatius was from a Catholic family.
Percy from the HP books' full name is
Percy Ignatius Weasley. :)