For me it's definitely Haak, Egonu, Boskovic in top three. Vargas is soon there but hasn't proved it yet, she is also more power but easier to "shut down" than those three from what I've seen so far. Call me out if Im wrong but isn't Vargas spike reach like 10 cm lower than the other three?
And I'd say Boskovic and Egonu are not as consistent as Haak but can get into a higher "god level" tier than Haak sometimes.
But to count out Haak from those three is weird to me, considering all of her achievements as Steven brought up.
Vargas is above all 3. She proved that many times last year with her consistent performance. We will see if she is fully recovered now, if she is she is on a level by herself above other 3. She is not as error prone as Egonu anymore, she is a better server than boskovic and Haak as well.