I've always pictured Astoria to be a Slytherin. After all, Sirius was just about the first wasn't he? Or something close to that. I agree with Molly that it is very cliche these days to put a Slytherin child into another house. If you were to, though, I think Ravenclaw (IMO) would be the best and probably only other option. Gryffindor is just.. Too contrasting to Slytherin. Sure, I think Gryffindor and Slytherin are probably the most similar houses, but it is the smallest differences, I think, that determine which house you are sorted into. Growing up in a Slytherin household would almost assure (with the exception of someone like Sirius) that you would behold similar values to them, at least when you are in school and when you are sorted. The Slytherin traits of cunning, sly, resourcefulness etc. Are probably traits that would be easily learnt at home.
Also, Hufflepuff from a Slytherin family? I really just don't see it.
So I think Ravenclaw would be your best option.
Wow, discussion of houses and house traits is a very important one to me. Sorry if I was repetititve above..
I picture her with brown hair and green eyes, I think. A slightly thin face, stern. I see her as being very nice and caring on the outside while having a bit of a temper sometimes, being slightly strict sometimes etc.
~ Annalise x