I have the Janome 8900 and really like the machine. But I haven't sewn on the others you mention. I have sewn on a friend's upper end Bernina and didn't like the feel -- can't be more definite than that. But the Janome just purrs along -- I swear it anticipates what I want and performs. Then again, I feel the same way about the Brother 1500s -- it is a fantastic machine, but only straight stitch.
The nice thing about the upper end machines these days is they tend to be durable and have all the bells and whistles. I purchased my Janome out of state, so I'm not sure how important a local dealer is as I don't have one and haven't needed any work done on mine. If I needed repair work done on mine, the closest authorized dealer is 4 hours away.