I have a sit down longarm and love it. It's more like quilting under a regular machine than on a stand up longarm, where you move the machine around. With a sit down you move the quilt. Good thing is, the sit down setup runs at about half the price of a stand up longarm and frame. It takes up less space, too.
I have a Juki QVP2200. They have just replaced it with a newer model, so you may be able to find a good deal on a used one.