If BFR is an option on the table, then I also don't see how Ultron can get wins against her, barring surprise or getting an attack in first (which, of course, would count toward his share of wins; but conceptually, Z should be able to make the majority here in that context.) Without BFR, Z might have more problems, unless she can first erect strong defenses and then finesse causing his systems to glitch/fail.
But if it's a standard fight, Z for the majority, situationally.