I would say a draw since they use to fight when they were a child, and they were kind of like Natsu and Gray ut they stopped fighting when the Lisanna incedent happened.
Well, at their prime, it would be a draw, but Mirajane was so distraught over Lisania that she sorta stopped caring so much. Erza didn't have to deal with that, so Erza worked hard. If Mirajane hadn't stopped, they would be matched, but Erza had been training while MIra had been posing for bikini pictures
