Short or Long Tube?
The long tube version has a longer focal length (think of it as light path). A longer focal length (again, light path) yields a higher magnification with any given eyepiece than a short focal length telescope.
The longer focal length telescope also requires less curvature in the mirror than a short focal length telescope. This usually translates to better image quality, especially at the edge of the field than the image produced by a short focal length telescope.
The short focal length telescope is more compact and portable, however, and with the lower magnifications it can provide with any given eyepiece, this version can be very useful for those looking for wide fields of view.