Cake tins are definitely better than plastic boxes for storage because metal is non-porous. However carefully you wash plastic, smells linger on. The previous occupant of a plastic container can taint the next, and mould can develop.
Also never store cakes and biscuits in the same tin, as the moisture from the cakes will make the biscuits soggy. For short-term storing an aluminium foil wrapping can be used, but if you're storing a rich fruit cake for a longer period, then use a double layer of greaseproof paper on the inside and foil on the outside – because the acid in the fruit can corrode the foil if it comes into direct contact with it and a mould will develop.