I've had the Janome MC6600 for several years, and I think it's a very reliable work horse. The instruction booklet is bare-bones, but I learned how to oil it (small circle you can see when you remove the bobbin case) and how to clean it (remove the bottom of the machine.
The thread occasionally jumps when I start a seam; I stop sewing and pull more thread down from the top threading, reattach threadto the moving guide, and continue sewing. I've never had it serviced, and it always runs well.
I learned how to do free-motion quilting on it and recently bought a Tin Lizzie LS because I love the actual quilting part so much. It's a good machine. Oh, Janome is coming out with a new model of the MC 6600, so you should get a good price.
Sharon