The first heuristic algorithm that jumps to my mind to solve this problem goes like this:
First sort the numbers into a list.
Second take elements from the head of the list to construct a subset A.
Third take elements from the tail to construct a subset B
The second and third steps are done in such a way that the sum of A and B are nearly equal. Then one can hope that this procedure make the elements that are still in the list to be near identical and so allow you to construct nearly identical sums.
The hope is that the remaining elements in the list l are similar in the sense that max(l)/min(l) is small, the heuristic could be improved one you try to make a trade off between max(l)/min(l) in the list and the difference between sum A and sum B.
