I think it's important to decide on your price range. That will eliminate a lot of machines.
I like
http://sewing.patternreview.com/sewingmachine/ for reviews of specific models because they are written by people who have actually used them. You have to join (it's free) in order to see all of the older reviews as well as the new ones. Most consumer places don't review the latest models and have different priorities than I do, especially in terms of quality, so I do not trust them as much. Personal reviews give more information about specific pro's and con's, so you can decide which quirk is likely to annoy you and which feature is going to float your boat.
I would personally rate the Bernina and Pfaff as the two highest. The Bernina purrs and is all-around totally solid on stitches, tensioning, and probably has the best quality machine quilting stitch. Pfaff is incredible for piecing because of its built-in walking foot.
Unless you buy their high-end machines, I would probably rate Singer and Brother at the bottom of the list. They have churned out a lot of low-end models that, for me at least, don't delivery quality. Some of their high-end models are loved, however. That's why I said at the beginning that you really need to establish your price range early in the process.