Space available for it is always a big consideration. Also figure out what kind of cash (or not) is available for the expenditure. Are you already familiar with the use of a long arm machine? If not, are you totally infatuated with the idea of quilting? If you are not a quilting fanatic, I would recommend against purchasing a long arm machine.
We are very happy with our Gammill machine! If you intend to quilt full-time (or close to full-time), buy the largest machine and table that you can afford and have room for!
Happy Quilting!