It would have to be on a stone by stone comparison and then it may still be difficult. You are talking about super ideal cuts which
they both are considered.
Brain Gavin was one of the co-founders of WF and help to create "A Cut Above" diamonds before he left to open his own company.
If you look at his Brian Gavins home About page you will get the story behind Brian Gavin and what he did before at WF.
For some reason I cant do any pasting in the window or I would give you the link.
I guess you can order one of each and see what you think. They are both cut to be top performers, but there may be personal differences, what you prefer possibly?
Superideal cut brands will be impossible to distinguish from each other by a huge majority of people. I guess maybe the cutters might be able to identify their own stones, especially if their target cut (angles, etc) is slightly different from another. But in general, they are extremely close.
I personally have dealt with WF on multiple occasions and stick with them because of their outstanding diamonds and sometimes slightly lower prices. Some people choose one or the other because they have the setting they want. Do you have any idea about the setting yet?
I don't think you will see any major differences between these two super ideal cuts. I have purchased diamond jewelry from Whiteflash and been blown away by the sparkle. More recently I bought a larger diamond and setting from Brian Gavin because they had the size, color, and clarity that I was looking for at the best price and it is a stunner. Two good options here.