SSD. Even if you don’t game or otherwise put your computer through heavy use, it will be much more responsive and will have a longer usable life. Mechanical hard drives have been the slowest parts of computers for a long time. I have laptops that are almost 10 years old that were once destined for the dumpster... replacing the HDD with a SSD removed the most severe limiting factors and breathed new life into them and to this day they are still perfectly sufficient for routine household use.