It's hard to make that decision because we've no idea right now what the show will actually look like.
How much is Andrew adding? The music, as it stands is pretty uneven and strange, Andrew's additions could turn it into a much more solid piece musically.
And what about interpretation? The other night Andrew was talking about comedians to play the scarecrow/tin man/lion. With the right casting, it could turn into a great show. There's lots and lots of potential there.
As for the Dorothys left - I would be happy with any of them. Steph is probably my least favourite left for the part, not because i don't think she's great, but just because she's a bit too sophisticated.
I actually think Sophie would be very nice in the part, especially after a few months training. She's got a lovely look for the part, has an innocence and sweetness that's very dorothy. The singing voice is good and the acting will come on with time.