Any organization can only be effective in relation to an objective. Non-profits and for-profits usually have different objectives and it is thus difficult to compare their effectiveness. If you are talking more generally of effectiveness and efficiency in terms of non-profits vs for-profits I would say that there are examples of very effective and efficient organizations on both sides of the profit line. If the question is asking to compare their effectiveness in relation to a single, unified objective, then I would say for-profit organizations are more effective because they are usually motivated by self-interest, which is probably the most powerful motivator.