I'd say a current SSD since there aren't any moving parts, but, that depends on the brand of SSD you have. I've had my 1TB SATA HDD for close to 9 years and it still works. My plan is to get a couple of 512GB SSDs and move the partitions to the new SSDs, zero out the 1TB HDD, and still use it for backups (SMART reports the HDD is still healthy as a horse).
As I said before, it depends on the brand, what you use it for (OS, games, programming, etc.), the pagefile set to the lowest settings (200MB will suffice), and trimming it constantly (Windows 7 and higher, and I believe XP, using the Smart Defrag program, can trim the SSD as well).