Very good question! You are right on the money! They are very different. The Am7 is small, light and very agile, perfect for off piste and rrail centres. The am9 will do it all, trail centres, all day mountain adventure and even the bike parks. So with this in mind they are both coming with me this weekend for my annual week at Afan.
I forgot to answer your question! I can't choose between them, they are both outstanding in very different ways, it purely depends on where I'm riding.