This cna be pretty confusion to choose from trumpet and alto sax.
This is basically the trumpet key. Generally speaking, trumpet comes in two types that is two category of keys one is Bb and second is C.
The Bb is a standard key that you will find in almost all the trumpet sold in the market. The Bb key is the modern trumpet key which gives a range of versatility in tone, music, volume, and sound. Overall, you can explore all the genres of music with this key.
A student trumpet is always a Bb trumpet as it is used for everyday practice for honing the skill and for playing different genres. We also recommend you to buy a Bb student trumpet.
On the other hand, a C trumpet is the less common form. This one you will find in professional bands. A C trumpet is a costly affair so on the student level, it is advised to stay away from it. Nevertheless, when you advance in your skills you can buy a set of this one too.
https://disappearsmusic.com/best-student-trumpet-for-beginner/