Use recursion when your data is inherently hierarchical/nested. Use iteration when your data is linear/flat.
In your case, there is a natural ordering you can impose on the combinations, so you can treat the data as linear, but if you view it as a tree you end up with the recursive approach.
If the structure of your algorithm reflects the structure of the underlying problem, you end up with simpler code that is easier to understand. Don't use recursion just because your CS201 professor thought it was So! Cool!
