I have the Juki 600 and love it, it's a nice sturdy dependable machine. The harp is about 8 inches so if you are doing large quilts it will be a struggle compared to the 11" on the Janome 8900.
I have the Janome 7700 and love it for quilting. I don't piece on it, I have a little Berinia 5mm machine that I prefer. I believe the 8900 is a 9mm machine and even the 7mm of the 7700 eats fabric on narrow seams so piecing on a 9mm would concern me.
You never really know how you will feel about a machine until you sit in front of it. I bought a Janome 6600 last year that I thought I would love but I did not bond with it but I love the 7700. My 6600 is for sale and was replaced by the Juki 600.