Buy used and buy from a dealer. If you buy a used machine from a dealer, they are thoroughly checked over and you get lessons, warranty and service for a year. You don't get that buying online or privately and often you are stuck. My advice for choosing one is to go to Viking, Bernina, Pfaff, Elna and Janome dealers and try out their machines. These manufactures are some of the best out there for any kind of machine. Sew on them, take your time and don't let them push you. Decide which one is a fit for you and then be prepared to wait for one. When I bought my first high-end machine I waited 6 months before I found the model I was wanting. My dealer finally said one was coming in on a trade and I was there the next morning with my deposit.
I like these dealers:
Bell's Bernina in Garland - I drive 25 miles past another dealer to him because he is so good.
Viking - in JoAnn's in Frisco - I teach classes for JoAnn's and I really like these ladies - Ask for Sherry, she is the best.
Janome - The Sewing Room in Frisco, across the parking lot from the Super Target by Stonebriar Mall.
I do not know Elna or Pfaff dealers but I do know their machines. Since I teach sewing I see and sew on all types of machines.
A comment about Brother, they do have a decent machine as long as you stay on the high-end. Also, I wouldn't touch a Singer with a 10 ft pole, they are finally starting to put out better machines again but I wouldn't buy one just yet.
Happy Sewing!