GDScript is not necessary better than any other language, its just different. GDScript is similar to the Python programming language, which can make it easier to pick up. That said, Godot also supports C#, which is a more common programming language (not Godot specific like GDScript) and has better performance currently. C++ offers even better performance through GDNative, but its notably harder to use.
Ultimately, it really is a matter of personal preference. GDScript is used commonly in Godot because its the most well supported, though C# now is pretty much on par in my experience. GDScript also was the only programming language choice in Godot for quite awhile, so most Godot users who have been using the engine for several years are familiar with it and use it for tutorials (which could be why C# tutorials are a little less common).
As with some many things: there is no “better” programming language, it is very much dependent on the programmers, the project, preferences, and what is needed to get something done.