Presuming all is specified reasonably well and performs well I would have said focal length over aperture.
Simply the moon has a habit of being fairly bright so you do not need aperture.
Go lunar observing and half the recommendations are get a moon filter.
So buying greater aperture to then add a moon filter to reduce the light gather is a bit pointless when you think about it.
But, remember that a telescope can't make an object appear any brighter than as seen with the naked eye. Telescopes only magnify, and given that magnification the surface brightness of an object will either appear to be the same as seen with the naked eye (nearly, ignoring any transmission loss in the optics) or dimmer (but never "brighter," regardless of aperture).
Furthermore, the perceived brightness of an object is limited by the size of your eye's dark-adapted pupil and all a telescope can do is fill that pupil by some amount as determined by the size of the exit pupil from the optic system. So, while aperture does play a role in determining the size of the exit pupil (as a function of magnification) that doesn't allow a generalization to the effect that a larger aperture will produce a "brighter" image (under all situations). It really comes down to the size of the exit pupil (determined by aperture and magnification), your eye's dark adaption, and the apparent field of view of the eyepiece (the latter a consideration if the object/moon does or does not fill the entire field of view).
Having said that, it's generally true that given any particular magnification and eyepiece a larger aperture will produce a "brighter" looking image. But, if you change magnification or apparent field of view with a change of eyepiece or have an exit pupil that exceeds the size of your eye'e pupil then the determination becomes more complicated. In fact, once the size of the exit pupil from the eyepiece equals the dark-adapted size of your eye's own pupil the surface brightness of an object won't change with increased aperture (since the light from that increased aperture won't be able to enter your eye).
Also, for completeness I should add that all of the above applies specifically to the viewing of extended objects (like the moon), since point-source stars do appear brightened with increased aperture.
Edited by james7ca, 09 October 2019 - 11:15 PM.