I have read over all the replays. As is my nature I must add my own 2 cents.
You have to test and test some more. Bring all the fabrics that you sew with and some others that you may or may not sew with that are difficult for a machine to handle. When testing be sure you are using the right foot for the job that you are testing, as it makes a difference.
I have both the 630Bernina, big sister for the 430/40/ 530/50
I love this machine, it is precise, goes through everything. FM really well. I have no complaints.
It does not have a big harp space as compared to the 7700. But I feel for an all around machine I much prefer a Bernina. Better buttonhole, feed is perfect, love the many feet and that the feet are stable never worry about getting through a think seam, Maneuvers really well.
But then I also have just purchased the Janome 6600, looked very carefully at the 7700 and opted for the 6600. One thing that weighted on me were some bad reviews, though some say that is taken care of. The other lack of power over multiple seams. But then after my dealer had it looked at the feed dogs adjusted it sewed fine. So if you decide you want the 7700, be certain this is done, or looked at.
As for the 6600 it is sewing over all kinds of seams so far no problems. I have had it for a week. First off I don't need a free arm, as I have the Bernina. I like this machine its, tried and true. It is rock solid, quiet, and easy to use. The Accufeed is a little cumbersome, but works great, once you get use to taking it on and off its super easy. I purchased the FMQuilting foot that comes with the Horizon, and also a blue dot bobbin case. Really if I were to pick between the Horizon and the 6600, and this was my only machine, then I think I would go for the Horizon.
So you see its not an easy answer. lol
Also all of the Accufeed feet except for the ruffler, pleater. And there is also a very cool and inventive foot that is a roller/tractor foot and comes with a set of different gizmos, for all kinds of jobs.
I love both of my machines. But if I could have only one I would go with the Bernina.
Only You can decide!