For bool, it can only be used in C++. (For C, there is only _Bool in C99 standard. ) It could be either true or false. It’s only true if it’s not 0.

For BOOL, it’s actually int as typedef int BOOL; and can be ither TRUE or FALSE. It’s only true if it equals 1.

For BOOLEAN, it’s actually byte as typedef BYTE BOOLEAN and only 2 bytes long.

For boolean, it’s not a formal type in C/C++.

Usually, bool is the most common one we use and takes 4 bytes. BOOLEAN is a better solution with less memory cost. But it’s still recommended to use bool in that I am already familiar with it.