Overloading operator

[GoDaddy]

Is it better to return a reference or a new instance of the object?

For example :

class A 
{

private : 
int seed;

A(int s):seed(s){};

A& operator + (const A &a); 
{
seed+=a.seed;
return *this;
}

A operator + (const A &a);
{
return A(seed+a.seed);
}

Which one is better ?