Hard drives are still the primary medium on the market, because of their gigantic capacites at cheap prices.
The downside to them is that they have a definite shelf life (only about 7-12 years, if installed and used correctly), so it's inevitable that you'll have to replace them eventually. Also, they lack in speed compared to flash storage.
Even with SSDs, you'll have to replace them eventually, as they only have so many read/write cycles to them. We haven't found a definite shelf life to them yet, so they are the medium of the future.