The result is exactly the same. Both represent the same type, so the resulting executables are completely identical.
The char keyword is an alias in the C# language for the type System.Char in the framework.
You can always use the char keyword. To use Char you need a using System; at the top of the file to include the System namespace (or use System.Char to specify the namespace).
In most situations you can use either a keyword or the framework type, but not everywhere. For example as backing type in an enum, you can only use the keyword:
enum Test : int { } // works
enum Test : Int32 {} // doesn't work
(I use int in the example, as You can't use a char as backing type for an enum.)
Related: Difference between byte vs Byte data types in C#