This is a necessary assumption, which is effectively asking which answer choice the author has to believe. Here we can prove that the author agrees with A. The author concluded that front loaders are better for some consumers because it is more convenient for them. Therefore the author must believe that the benefits of convenience in these cases outweighs the other factors that favor top loaders.
The author doesn't have to agree with C. In fact I think the author implicitly admits there are other important factors in the first sentence. It's completely possible that other factors are important, such as energy efficiency or quality, but that in some cases convenient outweighs those other factors.