C, 111 bytes

Full version:

//*
int main(){puts("Hello, World!");}
//**// i n t   m a i n ( ) { p u t s ( " H e l l o ,   W o r l d ! " ) ; }

Every other character

/*itmi({us"el,Wrd";
/*/int main(){puts("Hello, World!");}

C, 111 101 bytes

10 bytes saved thanks to Jasen

Full version:

//*
main(){puts("Hello, World!");}
//**// m a i n ( ) { p u t s ( " H e l l o ,   W o r l d ! " ) ; }

Every other character

/*mi({us"el,Wrd";
/*/main(){puts("Hello, World!");}