@Ralph ,
@PHolder is correct. If you could elaborate on your purpose a bit more, we could elaborate on answers. NAS drives have one strange attribute that I'm trying to remember but I cannot. Something about buffers, maybe. It's not coming to me. Maybe someone else can chip in. But, that might distinguish them from say, a video recording drive. HDD's are mechanical parts and always moving the platter and the heads, and will eventually wear out. If there are no surface defects and if the heads keep flying like they should and if they're not subject to excessive vibration and physical abuse, HDD's can last a long time. They can retain data for long periods of time when dormant. HDD's need periodic defragging. HDD's are subject to data loss from power failure, power spikes, bad cables, etc. Look for a long 3-5 year warranty from a reputable company and possibly a pro or industrial model. I personally like to burn in my HDD's by filling them with encrypted junk data and hitting them with a level 4 pass with SpinRite. That should produce no errors and no reallocated sectors. But, all machines fail eventually. HDD's are no different. They generally fail when we're least prepared and least want them to. Just cosmic karma, I guess. Asking what the best hard drive is is like asking what the best car is. It's been a while since I've bought any but I tend to have affinity for the pro grade or at least prosumer grade versions from Western Digital and Hitachi. If that has changed in recent years, someone let us know.
SSD's, under the right conditions, can outlast HDD's. Having no moving parts is an advantage. They are probably more susceptible to power problems and are definitely less susceptible to vibrations. But, as you said, they're write limited. Every time the memory cells are written, they punch electrons through an insulator on top of a microscopic capacitor. All those lovely terabytes of data are just a bundle of electrons in trillions of little capacitors. As the storage medium ages and gets used, those insulators degrade. Once the write limit is reached, the data is more likely to encounter bit rot or literally just fade away. That doesn't happen nearly as much with HDD's. You have to look at the SSD's Drive Writes Per Day or Total Bytes Written or Terabytes Written specification. This MAY be different from the warranty. While in operation, that limit should be monitored. That can sometimes be done with software for drive maintenance from the manufacturer. IE, Samsung Magician, etc. Once you get close to the drive's write limit, the data should be removed and it should be decommissioned. I've read that some drives will shut down when the limit is reached. That would be an unpleasant surprise. I would, again, look for pro or industrial grade units with long warranties from reputable companies. I like Samsung SSD's, but I'm sure there are other good ones too. This is controversial, but I also burn in my SSD's by filling it with data and doing either a level 2 or level 4 pass with SpinRite. Note that doing this with level 2 will use up 1 full drive write cycle and doing it with level 4 will use up 3 full drive write cycles. Filling it with data takes 1 and level 4 SpinRite adds 2 more. It is important to leave SSD's at least 10% empty and unpartitioned so the drive can do it's housekeeping work and maintenance work better. This is called overprovisioning. Some drives have this built in. Some don't.
Also, in some cases, it's possible to dramatically reduce the writes to an SSD with write caching and storing temp files on a ram disk or a separate HDD, etc. The more things you cache, the more you have to be concerned about power protection and not allowing ungraceful shutdowns. Whether SSD or HDD, it's a good idea to do a level 2 SpinRite check one or two times per year.
Given the state of the world and the universe, the following might be relevant from a physics, not political, point of view. Should one find themselves in the midst of excessive solar storms or nuclear weapons attacks (far away), the media of a HDD may be more survivable than the media of an SSD. Of course, if that's happening, we may have bigger fish to fry than what's on our storage drives. Depends on how important the data is. The electronic controllers and the computer itself will be much more vulnerable to such things.
Hope this helps. There are always many ways to solve a problem and many pros and cons.
May your bits be stable and your interfaces be fast.
Ron
