There are several questions I would ask, agree with Pumpkin Patch, what do you intend, business or just plain Fun!
Business, I would get a machine with a frame you can grow with. Gammill Vision can be 22" to 30" depending on the throat of the machine. I have an optimum but had traded up to this size. I love the new track Gammill has, don't have that, but its really nice.
I so often see people who purchase a machine and it isn't what size they needed for their business. So think big!