I really recommend trying a few machines out, there are differences. I also seriously recommend getting a stitch regulator with your purchase (can be much more expensive later if it is an option) and if you have the budget get a computer driven one. Also look at how adjustable your frame is, especially if you are taller or shorter than average. You can get sit down frames if desired or high wheeled chairs for standard frames for that matter.
The set-up I use belongs to a friend of mine. Grace frame with a Pfaff P3, no back handles for using it with pantograms and no computer. It's rather lovely compared to stuffing a quilt though a standard machine, but not everything as easy as my friend hoped it would be. Still a bit physical for her, so far I've used it more than she has.
The frame set-up can be a bit complicated and I think really needs two people and a long level. I don't know if any are designed to be easily taken up and down, so make sure you have the space you need, the length/width of the frame and at least 3 feet around each side. We have moved and reset my friend's system ourselves. The long arm itself was pretty heavy and awkward but all of the frame parts were easily moved by out of shape women of the plump and 60ish persuasion...
Personally I like the 12-foot size but then I pretty much work on bed sized quilts. I think my friend's is a 10-foot, it's plenty big for her and has so far been fine for my queen sized projects. It is two sections and when she tried just setting it up shorter it was just too small even for the more lap sized quilts she makes.