Mounting-wise, I'd go with either 2 or 3. Just from looks alone, I'd go with either of those. The benefit of two over three is the linear gripper, but three appears to have better clamps (again on looks alone.)
It's really hard to say without having used them. Just based off of my past experiences with similar machines, I'd go with 3, personally. The jump to the forth (the electric) is a decision you'll have to make. I wouldn't touch it if it doesn't come with a good warranty.
Michael A. -- If your flaw in stringing is consistency, http://www.youtube.com/yulitle
MRT 07-08 -- your stringing will be consistently flawed.