Both statements are correct: aperture is the most important factor, and many large aperture telescopes are resold due to lack of use.
The brightness of any object you observe is determined by the aperture of the telescope ("light grasp"). With larger objects, such as planets, the aperture also determines the resolution: the amount of detail you're able to see. As you increase the magnification (by changing eyepieces) you'll notice the image will become dimmer, and after a certain point it will also become blurred and will lose detail (atmospheric disturbance, which changes from night to night and from minute to minute, also affects this).
The trick is to get the largest aperture telescope that you will actually use, and this is very personal:
How heavy a telescope can you physically lift and carry outside?
For many people, as they get older they can't carry heavy things as easily as they once could. For this reason you see many amateur astronomers downsizing when they get into their 70s.
Where do you live?
There's a big difference between opening a door and wheeling out a large telescope, and carrying a 35kg metal tube up and down several flights of stairs.
What are the skies like where you live?
If I put my 250mm aperture telescope alongside my 80mm aperture telescope then the views in the larger aperture are a lot brighter, (and bigger, due to the longer focal length). But I can easily carry the 80mm up a mountain and away from light pollution, and in those conditions I'll see a lot more with it than my city-bound 250mm will show me.
Do you have a car?
My 250mm reflector fits perfectly on the back seat of a car, and in two hours I can be far away from the light pollution; but I personally have to hire a car if I want to do that.
You'll need to weigh up all of these considerations, as well as your budget, and when you've done so the perfect telescope for you should become apparent.
When I performed this exercise before buying my first telescope it was clear to me that a 10-inch reflector on a Dobsonian mount was the right one for me: I live in a city, I have a wide balcony, and a limited budget.
And if you come to the conclusion that you have to get a telescope with a relatively small aperture, but you live under heavy light pollution, then don't be disheartened: instead look into "electronically assisted astronomy" (EAA) - using a small telescope, a sensitive astro-camera, and a computer, you'll be able to detect objects that your eyes alone would never be able to see.