Its stated numerous times that they're equally strong in the power, or at least so close as to make absolutely no difference. I don't know if the same can be said for Elayne and Aviendha, though I'm fairly confident in making the assertion that Egwene is far more "refined" than any Aes Sedai (with perhaps the exception of one or two). Not in every area, of course - Egwene possesses little to no skill in Healing, for example. Nynaeve, in contrast, is relatively unrefined though highly skilled; her weaves are not very precise because, generally speaking, she's relied on raw talent, potential, and power. Were she to duel, say, Semirhage, she would lose fantastically - though Nynaeve is more powerful than Semirhage, she lacks precision and refinement.

I believe Egwene, though certainly the weaker of the two, could match Moghedien. Perhaps not defeat her, though Egwene would definitely make Moggy sweat.