Hi,
For planetary viewing, aperture rules.
As long as we are comparing equipments of
equivalent optical quality. There is no point comparing an apo to a dob since the apo has excellent optical quality and the dob average optical quality.
For a given night (= at a given seeing) there is a max useful magnification no matter the instrument type.
On a turbulent night, all instruments type perform the same (same maximum useful magnification). Smaller instruments might display an aesthetically more pleasant image due to the smaller aperture "seeing" less turbulences. A bigger instrument can be reduced in aperture to match the smaller one and will deliver the same images.
Under good seeing conditions, a small instrument in aperture might be limited by its resolution (below the maximum useful magnification on that night) whereas a larger instrument will not be.
A second parameter to consider is brightness and contrast. No matter the seeing conditions on a given day, a larger instrument will obviously deliver brighter images, which in turn helps seeing details of low contrast.
Consider the following images:
http://www.astrosurf.com/altaz/images/image020.jpg
Obviously, the details are easier to figure out in the brighter images.
This is why, for planetary observations, aperture (and optical quality) always rules.