Fundamentally from the perspective of natural selection there isn't any reason to distinguish between 'long-term' and 'short-term' in such a broad way, without clarifying what you mean by short and long term, and particularly without mentioning the survival benefit of the adaptation.
The reason for this is that is a trait has a very powerful survival benefit, even if that benefit only lasts for a few hundred years (the stronger the benefit, the less the time required for the adaptation to become fixed, a 100% survival benefit would become fixed effectively instantly) there is a high probability that it will become so abundant in a population that it will drift to fixation eventually. Conversely, if a trait has a benefit, but that benefit is very small, then even if the benefit lasts for millennia, if the population size is large, it probably will never become fixed.
The way to think about this issue is to realize that the actual process of evolution happens over very short terms, based on adaptations that are beneficial 'right now', and that that process is actually a relatively weak one, particularly for smaller benefits. Because the process of natural selection is quite weak on all but the most powerful adaptations however, the longer that an adaptation is beneficial, the more time evolution has to act. For the homework question, the difference between short term and long term are irrelevant, the question is actually asking about the heritability. However, in your question 'Which one contributes more to evolution', the answer is that if everything else is equal, adaptations that are beneficial for longer will be more important to the evolution of a given organism, because evolution has more time to work. However, I hope you can tell from my answer that the question is a gross oversimplification of the processes of evolution, and other factors are actually more important.
As an interesting aside, a good example of something like this question in action is present in the tropical regions of the world. The tropical rain forests of our planet are old. Very, very old. They also happen to contain the largest species diversity of any region on the planet, with the result that the vast majority of tropical species have very tiny niches - which is the reason they are become extinct so quickly in our rapidly changing climate. A very plausible theory for this diversity is that given the huge amounts of time the rain forests have existed, even small advantages in a given niche end up becoming fixed in a population, resulting in extensive speciation. In other parts of the world, where ice or desert occasionally kill almost everything, there just isn't the time for that kind of super-specialized adaptation to occur, and so there are fewer species.
