Martha, I feel your pain! I have a 153QE that I think is about 6-7 years old. It has been in the shop more than my old 1090 ever was, and now the tension is screwed up again and free-motion quilting is a crapshoot. I am heading to a dealer tomorrow that carries Bernina and Janome, hoping to trade it in on one or the other.
I have a theory - my 153 was what you would call a "middle of the road" machine (for a Bernina). I think it was about $1800 new. I think that they cram all of the features (stitches, etc) that they can on a machine, and that the quality suffers. I do not think the straight stitch on this machine was EVER all that perfect, and the decorative stitches were unreliable - ten would look perfect, and then the 11th would have bobbin thread showing through. It was frustrating, and the dealer would take it, work on it, show me a line of 50 decorative stitches they made which were perfect, and then a month later it was out of whack again.
I bought the Bernina because I use my machine a LOT. This year, I have finished 3 baby quilts and 4 twins and am working on a queen.
I am considering a Bernina 430 or 440 or a Janome 6600P, but am now wary of the Bernina (I know, heresy!). I have a friend who has the Janome and loves it.