I love my Brother NX600 - it's about 9 years old now but have never had a minute of trouble with it. I also have a Viking Iris, which I leave set up just for embroidery (but it is for sewing too). My issue with Viking though is everything extra for them is SO expensive !! Then I have my Janome 6500 Memory Craft Professional, which I LOVE !! I have never had to adjust the tension for FMQ on it.
Just do what everyone says and test drive.....