Due to her showing up late in GT, I feel Oceanus may be the strongest female in the original trilogy. Great interesting character with peak design as well.
Android 18 is probably second. I feel she's a bit stronger than Pan. Having that unlimited energy gimmick probably helps as well.
Pan seems like the logical choice for 3rd place.
But after that it gets interesting. Would it be Videl? We don't see her fight in GT, but she appeared fairly strong in Z.
*I specifically excluded Super from this, as the added women from from that show would make it far too easy. It also wouldn't be "compatible" with the original trilogy, timeline wie.