Thanks for the nice compliment. In general, my opinion is :

External HDs are unlikely to be as reliable as internal HDs - not always, but usually. Why?
1) it’s difficult to determine the quality of the HD in a prepackaged external, and it’s usually the cheapest drive in the product line.
2) the cooling is unlikely to be as good. There’s likely no fan, and if there is, it’s smaller (lower CFM) and smaller enclosure and external ports to exhaust heat
3) if it has a power supply (not powered by USB from the computer), it’s typically a poorly regulated and protected “wall wart” unlike the higher quality PS in the computer
4) there’s the protocol conversion to USB and back to SATA plus two physical ports, and the USB (or other) cable - all potential failure points, not to mention the USB driver.
5) many/most popular externals are in the $100 or less range. I contend that you cannot build a quality HD, case, interface and power supply, QC it, market it and have the reseller make a mark up for $100.

If you want an external, buy an enterprise quality drive, a case with a fan and a quality power supply, and assemble it. It will take 5 minutes max, you may spend over $100, but it will be quality storage.

Now as far as SSDs vs HDs:

1) the SSD is orders of magnitudes faster in every respect, but you may not need that for backup or archive
2) initial testing shows them to be more reliable than HDs providing it’s made by a reputable manufacturer.
3) smaller, less heat, insensitive to shock/vibration.
4) the limitation on the max number of write/erase cycles is irrelevant for home users. A ITB SSD typically has a spec of 150-600TB written. How many people ever actually write 150 TB to a drive? Nobody, but an enterprise server handling multiple users.
5) although they will retain charge for a LONG time, I’d power it up every now and then.
6) they do fail even if not as often, and when they do, they may fail quickly and be unrecoverable. In fairness, HDs are not cost effective to recover unless the data is VERY valuable, plus, you ought to have another copy or two of your data for backup and disaster recovery anyway.
7) consumer quality HDs are cheaper in terms of $/TB (and enterprise drives less so) tha SSDs, but the cost/TB of SSDs is dropping by ~ 1/2 every year.

The net-net is that if you’re using the drive for the OS and application, the SSD is a no brainer. And if you’re using it to store data, it’s still the best choice unless you have many TBs of data (a quality 2TB SSD is $140 - next year it’s likely that you’ll be able to buy a 4TB for nearly the same price). Personally, all my computers have been all SSDs (including backups) for ~10 years. I use all Intel or Samsung SSDs and have never had a failure - I have 10 year old SSDs made by Intel still in service 24x7x365.

Hope this helps.