Is it preferred to put statements inside an else statement or use multiple else-if statements?

Hopefully a simple question: I was just wondering if there was a convention for putting multiple statements inside an else, or using else-ifs. So, is it generally preferred to use an else statement with statements inside of it, like so:

if(r>0){

    return x;

} else {

    if(completed==false){

        return y;

    } else if(started==true){

        return z;

    } else{

        return xx;
    }}

or to use else ifs, like so:

 if(r>0){

    return x;

} else if(completed==false){

    return y;

} else if(started==true){

        return z;

}else{
        return xx;
}}