Rubber or leather? For myself, I answered this question like this: both, and that!) Depending on the situation.
Let's consider this question on a number of examples.
As you know, not every leather "loves" water. This means that if you swim in a watch with a leather strap, there is a great chance of ruining your leather, especially if it is not properly dried.
If the thread of the firmware and the glue are not particularly afraid of water, the leather may become deformed, lose color saturation, or even crack.
But many lead an active lifestyle, swim in hours. That's it, they will be fine with a rubber strap.
It is rather soft, not afraid of water, easy to clean and has excellent wear resistance.
For example, for traveling to the sea I put on a watch such a set: a rubber strap and a buckle "Marine mine".
It also happens that a rubber strap was initially installed on the watch, but it was rendered useless. This is a good opportunity to switch to natural leather.
We put a new strap and watch instantly transformed, become more strict.
Or you wear an hour on a rubber strap ...
But accidentally see the leather, which you can not pass. And you know that with her your watch will look much steeper)))
In general, the choice is always yours! ;)