Egwene might have strength in all five flows, has the greatest mastery of combat weaves and in general, is the closest thing to a channeling expert of all the female channelers on the Light-side. She can modify weaves on the fly to accomplish things. While Elayne and Aviendha could learn the same skills, they never showed the same potential for mastery Egwene has. In addition, the Amyrlin Seat is in command of an organization of channelers - time for training is built into her set of responsibilities and she has access to cutting edge researchers (such as Elayne or Nynaeve) any of whom would need to illustrate new weaves to her in order to share information.

Elayne learns quickly and is smart enough to learn all the defensive weaves from Egwene she can. She'll be an expert, but I think her duties as a queen and mother will prevent her from reaching the level of mastery that Egwene has. She'll come in second.

Aviendha would likely be very restricted to the use of the One Power, and since the duties of a Wise One really don't have much to do with the One Power, she'll be very limited to how she can handle her strength - she's learned from Egwene, Elayne and Nynaeve, but not the level where she is currently a match for them.

Thus in a fight involving only the One Power, I think Egwene would be 1st, Elayne would come in 2nd and Aviendha would come in last, in order of effectiveness.