Planets want resolution and galaxies want light, and a lot of buying advice treats those as opposite requirements. In practice one instrument serves both, because the specification that supplies each of them is the same one: aperture.
Where the two requirements agree
Aperture increases both resolution and light grasp. A 200mm instrument resolves finer planetary detail than a 130mm one AND shows fainter galaxies, so the single decision that most improves both is the same decision. The apparent conflict comes from focal ratio and mount, not from aperture.
Where they genuinely differ
Galaxies want a dark sky far more than they want aperture: a 130mm instrument under genuinely dark skies shows more galaxies than a 250mm one in a city. Planets are almost immune to light pollution and care instead about atmospheric steadiness, which is often better in a town than on a windy hilltop.
The practical answer
A dobsonian of 150mm to 200mm, which is why it is recommended so relentlessly. It gives the aperture both jobs want, the mount is steady enough for high magnification, and the money that would have gone into a tracking system goes into the mirror instead. The one thing it will not do is photograph deep sky objects.
Questions people ask about telescope
What is the best telescope for viewing planets and galaxies?
A dobsonian reflector of 150mm to 200mm, for most people and most budgets. It supplies the resolution planets need and the light grasp galaxies need from the same mirror.
Can one telescope do both?
Yes. The conflict is usually presented as real and is mostly about mounts and portability rather than about optics.
Does light pollution matter for planets?
Barely. Planets are bright enough to cut through it. Galaxies are the opposite: a dark sky helps them more than any amount of extra aperture.