Well, I have a difference of opinion (wouldn't you just know?!).
To me, a nine patch block is the last block I'd ever use with sashing because.....nine patches chain diagonally across a quilt, giving the surface interesting diagonal eye appeal and movement, especially when they are set beside a plain alternate block. Sashing tends to break up this design potential and can make the quilt a bit more "stagnant" (in the literal meaning of the word), in my opinion.
That being said, it is only "my" opinion and I think any quilt is wonderful; yours will be too, no matter how you do it!
Jan in VA