Everyone seems to read the series and they try to make a scale for themselves regarding how strong the channelers are. It all comes down to interpretation. Anyone who says that their strength list is irrefutable is massively incorrect, because even people who read this stuff all the time have to rely on speculation for the most part.

There is only one irrefutable type of statement i.e. when a channeler who is at full strength comments on the strength of another character who is at full strength. This phenomenon is rare, but has happened in the case of Graendal comparing herself to Cyndane, for instance.

The problem with our Egwene-Nynaeve comparisons is that we've never had direct comparisons between the two, and most importantly, they both spend most of the series building up their strength and commenting on how strong they are at the time. Even if we Egwene comments on Nynaeve's strength in the next book, we still need to know if Egwene is at her full strength, and if Nynaeve is too.

Only a year ago, almost no one would have contested that Semirhage and Mesaana had similar strengths in the Power. Mesaana compared herself to Semirhage and said that they were relatively similar. We now know that Mesaana is weaker than Semirhage, despite one of the stronger statements we've had regarding two Forsaken comparing each other. RJ always said he wanted to keep it vague, and this is proof. To compare Egwene and Nynaeve at their strengths at that time based on a quote to power a ter'angreal is just as erroneous.

Anyway, I've been in tons of these debates, and I'll always think Nynaeve is much stronger than Egwene. My simple proof is this : Alivia is said to be considerably stronger than Nynaeve at that stage. Nynaeve was at least as strong as Moghedien in TSR and thus even stronger in WH when this comment was made. This means that a woman can be much stronger than Moghedien. There are only six women stronger than Nynaeve, so it makes sense that Nynaeve is very close to the upper strength limit. Considering Egwene can never reach Moghedien's level, it makes Nynaeve much stronger than Egwene.

Unless you believe that Lanfear is half again as strong as Nynaeve for some reason, or that Reanne was wrong... or some other reason you have your own beliefs. That's my 'academic' reasoning for it anyway. I've also got the general impression that whenever Elayne or Egwene have wanted to describe something indescribable or monumental regarding the Power, they've referred to Nynaeve. Their statements convey a sense of awe, as if they could never approach that level even from a distance. Other readers may feel differently.