Wel consider what you gonna use it for. Are you gonna primarily use it for making models and small items. Or will you have the need sometimes to take care of bigger jobs?
I bought a so called gunsmithing lathe, its kinda big. But it will handle bigger work. Although most things i turn is really small items. But sometimes that odd job comes up that calls for the bigger machine. When deciding for a lathe. you need to consider what you will use it for primarily and what you wanna be able todo if the odd job comes up.
Are you gonna turn kingpins for the spindle on a car project. well you probl not need the dimensions of the larger lathe but you will need a higher torque/speed machine. Are you gonna do gunsmithing work on barrels for the odd job - well then you need the length and size, but you arent really in need of the higher torque..
What im trying to say.. Think lateral.. one step ahead and dont focus on your current needs, think about what you wanna be able todo. The lathe is a really versatile tool. And prob. the most used in your shop efter if u get a mill or 2, the lathe will always be the one tool you will prob. use most when you get comfortable with it. =)