I have quilted queen size quilts on a cheapie Brother machine from Walmart. I think it's all about the walking foot. A good walking foot makes it so much better.
My advice is to figure out what the most important things in a machine are for you. When I bought my new machine, I was looking for more throat space. My cheapie Brother has all the fancy stitches I will ever need so I went with a straight stitch only in order to get an 11 inch throat.
If FMQ is your goal, needle down is a great option to have.
Do you plan to take it to classes? If so, make sure you can carry it.
Start asking yourself exactly why you want a new machine. Whatever that reason is, is likely the most important feature to shop for.