Hey, from studying Minagi and Ryoko I've come up with a final opinion on who 
would win in a one on one fight.  

    First of all, Minagi only posseses Ryoko's ablility to fly.   She lacks 
Ryoko's ability to summon up creatures, as well as Ryoko's well known ability 
to teleport.  She probably also lacks Ryoko's ability to transmutate things.  
Though, Minagi lacks all these things she appears to have a greater fighting 
skill, though she may posses a lack of experience over Ryoko, and also her 
sword seems to be made better.  Yagaki designed Ryoko's sword, so odds are 
that he simply made Minagi's sword more powerful.  Minagi's true power seems 
to exisit in her sword.  Her sword can generate electricty and she can 
increase and decrease it's voltage by will.  This is most likely why her 
sword was overwhelming Ryoko's ,because she most likely increased the voltage 
with every strike.  This is most likely also the reason why Ryoko's 
lightining didn't affect Minagi.  Since, the very source of Minagi's power is 
electricity; she could probably overwhelm it with her own.  Also,  Ryoko 
seemed to be stronger physically over all.  As Ryoko's punch from out of the 
water devistated Minagi ,and also Minagi wasn't able to recover when Ryoko 
threw her even though they were sitting there for quite some time(probably 
about a minute and a half.).  So, overall i'd have to say that Ryoko could 
probably beat Minagi in a one on one fight if she used all of her powers.