this is what i would do if i was buying a machine now...go to different dealers and try their machines and try all kinds with different features that way you will find what you like and need in a machine. Take your time and dont rush into it...Talk to lots of people..go to a local quilt group and see what they use thats where i found lots of useful info after i bought my machine...
Buy from a dealer and get lessons so you can use your machine to its fullest. Also get to know your dealer so when you need to service your machine or get it repaired you need someone you trust. Find out how much a machine is to service as the computerised ones cost more to service..
these are all thing I didnt do and definitely would do as a machine is expensive and an investment. Look at used ones as i bought mine used a couple of years ago and have had no trouble.
The features that i would look for are what feet come with machine and if you love quilting try to get a walking foot thrown in as they can be expensive!! Also see if you can get a 1/4 inch foot and a darning foot thrown in as these are all feet I had to buy afterwards..
Decide what you need in a machine ie do you really need an embroidery machine as a lot of the machines come with so many stitches. i bought a Bernina Artiste 180 with embroidery hoops and all but have not used the embroidery bits at all yet as i have not had lessons and the shop i bought from i found out afterwards that the guy who owns it is not trustworthy (this i heard from several people afterwards)
I do love my machine and even if your machine is basic try to get one with the needle up/down feature as that is one feature i do love on mine. Also when testing machines some are noisier and some are smoother so look out for that as well. Another thing is throat space.. get a machine with as much throat space as possible if you have a choice on that.. Good luck in your search and let us know what you end up with