I wrote elsewhere:
There are endless discussions and tips on antenna types and reception optimisation, which can sometimes overshadow the basic advice “make sure that you have a clear view of the sky”. If a picture can say more than a thousand words, here are two pictures to make that point:
The image on the left was made with tar1090 and shows all the tracks recorded by my feed in the preceding eight hours. The black dot on the image on the right shows the position of the antenna.
The antenna is the absolutely simplest possible and sits on the balcony railing of a 3rd-floor apartment in a six-floor building, essentially half-way down an urban canyon. Look at the direction of the street and compare it to the spread of the recorded tracks. That £5-antenna has been picking up signal from 100nm away where the view is unobstructed, but can’t even reach 20nm out across the street.
Until I saw that track spread, I was pondering getting a better antenna, a preamplifier, generally better equipment. Looking at the spread makes it clear that just moving the entire rig to the roof of the building will do a world more good than throwing any pile of money at it in its current location. Especially since this happens to be the tallest building at the very top of this particular hill.
Ergo: a clear view of the sky beats a good antenna hands down. Having both is ideal, but a clear view should always be the first priority.