It actually highly depends:
If you look more towards the top of your screen, you can see fruits faster. This is good for high AR, wide spacing in between fruits (more important for small fruits) and streams. You have more time to evaluate a general movement path to catch fruits here, but you mostly estimate the exact positioning of both your caracter and the fruits.
If you look more towards the bottom of your screen, you can be more precise, being able to evaluate where your catcher catches fruits and small adjust your positioning accordingly. You are able to follow the movement of the catcher much better in this case and only have to look at the next fruit you are going to catch as opposed to looking at most of the fruits on your screen. The drawback here is that you have to search for the next fruit, which costs time and ultimately leads to slower reading.
Also, there is a difference in between seeing every single fruit or just the shape they form, depending on how much you focus. Seing shapes is faster, since there are naturally less shapes (aka movement patterns to be done) on your screen than actual fruits and you don't actually have to evaluate all the fruits in order to see a shape (think of sliders or streams), which in contrasts leads to estimation errors sometimes. It comes down to which method is faster: If a movement pattern shape is common for you, the map has a natural flow or you just played a map a bunch of times, it is easier to see these shapes but when there is antiflow, weird patterns or a fruit you always miss, it is easier to look at each of the fruits separately rather than looking at each of the fruits and then forming a new movement shape out of them. Looking more towards the top of the screen tends to have more of the less stressful shape seeing approach in contrast to looking down beeing more the full focus evaluating every single fruit approach. And focussing is like zooming in, meaning being worse for long distance hyperdashes. The catch is that you might not have the time for using the single fruit approach depending on high AR or long endurance weird patterns but you also might make more estimation errors using the pattern method. This game is all about pattern recognition both visually and audible plus hand brain coordination.
In the end, it doesn't even matter. You end up somewhere in the middle anyways.