I'll like to rephrase your question to "what is the difference between viability and deficiency and which would I rather choose to be"? Powerful or productive? I don't think viability can interprete to productive or being powerful, it means a state of being able to be achievable for example as human beings we know the things that we can achieve and the things that we cannot because we have made measurements of ourselves and our capabilities before we can decide what is actually achievable and when we consider something achievable it means that that term is actually viable and viability can mean possibility of actually making something come to pass or come true.
On the other and efficiency means the ability to be efficient, possibly successful, viable and up to par in all circumstances. When someone is in a state of efficiency it means that they are productive just like you have stated and that productivity can actually bring them a sense of power which can actually make them consider themselves powerful. If you look at countries like the united states their level of efficiency in making things possible is the reason why they are considered the most powerful nation in the world because difficult things seems viable to them and as a result of this they have attained the level of efficiency which brings that feeling of being strong and powerful.
So if I were to choose I will definitely choose to be efficient because efficiency is the last stage of viability before someone can be efficient he or she must have gone through a process of viability so many other process of hard work and the sense of fulfillment which makes them trustworthy at all moments. But nevertheless I will choose to be efficient because like you said it makes one productive and develop a feeling of being powerful