I don't have a Janome, but I'll give you some advice anyway!
Sew on all 3 machines, bringing your own fabric - including a quilt sandwich for free motion, some piecing, and machine applique. Even if it's something you don't think you'll be doing, because you never know when you'll want to learn something new.
You can read reviews on the internet, but until you actually experience the machine you won't know which one is right for you. I have a Bernina 440 and a Sapphire 850. I'm still kicking myself for buying the 440, which I love, before I knew about the Horizon. Even if I didn't buy the Horizon, I would have liked to try it out.
I have friends who swear by Bernina, and I have friends who are as fervent about their Janomes.
Janet