A lot depends on how many photos you have and want to save. A hard drive offers more/unlimited capacity but as you rightly point out there is the possibility of damage. Also what if the drive were to become "corrupted" which is RARE these days but can happen then it would have to be a "specialised" recovery.
If you were to use SD cards then you could use as many as you require - so for instance if you had 4 cards in total and one became "corrupt" and your priceless photos were "inaccessible" then 75% of them would be "safe".
Any disc or card is subject to possible "failure".
but I have only ever had 1 HDD failure in over 20 years ! (But I had a backup)
So to sum up - 1 backup is better than none - 2 backups are better then 1.
My method is to use 2 internal HDD's and CLONE every 2 or 3 days - you could do the same with an external drive - it works for me.