Like Digerati stated, one has to be diverse with backup, it can be in several ways. One of mine is to rotate retired yet still great running 1TB HDD's that's in aluminum enclosures, avoid plastic because these retains heat & possibly cause backup image corruption.
Since the 'shortage' of HDD's that never was, just higher pricing, I jumped onto the SSD revolution & have never looked in the rear view mirror. Meaning that I had at the time, three 1TB HDD's less than a year old, and all were performance models. Have since acquired more computers & therefore more SSD upgrades, freeing lots of space for backups.
Another practice to avoid for one's security, only have the external plugged in when performing a backup or transferring data, have a couple of smaller (500GB) models for the latter. Personally, I don't prefer to mix data with disk images, though that's me.
As to which software to use, Macrium Reflect is the best free choice & there's a couple of reasons why. First, WinPE is now the only option to create rescue media that can be booted from and perform backups outside the Windows environment. Secondly, open the Macrium interface, and under 'Other Tasks', there's an option to add Macrium Reflect to the boot menu, which is a lot faster than a CD or Flash drive, all one has to do is attach the external beforehand & create a folder for the backup. Then reboot to the WinPE environment, and the option for Disk Image will be there in no time. It's so simple, a teenager who is computer literate can use this software.
It's basically after booting & select Disk Image, select the drive to backup, underneath there'll be two options, clone or image the disk, choose Image This Disk, then choose that folder created for it to go into & Next, look over what has been chosen & click Finish, and the backup will begin, the last choices on the bottom while backup is running will be to shutdown, reboot, and a couple of others I can't recall at the moment. If shutting down, will make sure to turn off the power switch (if one) when the system shuts down or reboots, or if a 2.5" drive w/out a power button, remove the cable, because sometimes the computer will reboot anyway.
As to backup on SSD's, I haven't went that far yet, preferring to use these where needed the most.....installed in my one of my computers. However, I realize that a newer type of portable SSD has emerged, which can be used for backup. The only thing I don't like about these are the connector, it's not a standard SATA one. If I were going to do this, would purchase a SSD on promo, as well as a USB 3.0 (or 3.1 if needed) enclosure, this gives me an option of what to do, should the enclosure's connector goes bad. Without that, the retail portable SSD is worthless, same with newer versions with a HDD. All it would take is it falling & landing on that end with the cable inserted, the drive is toast. It's not like the old days when we could remove a HDD from a plastic enclosure to place in a aluminum one, or to install in a computer anymore.
So I recommend, if you want to backup to SSD, make your own. I've only purchased one retail backup drive in my life & that was years ago, though have been given many where the owner thought was dead, or found in the recycle bin shared by 16 apartments, most every drive ran fine once opened & installed in a computer or other enclosure. These OEM's often uses cold soldering of the contacts & these will often break, especially if moved a lot or overheated by leaving on all the time.
Hope that my post has been of assistance in your decision.