If you have backups it doesn't matter much what you buy. It's not like there's much choice anyway. :)
Do you want to buy a small 2.5" one? Or a larger 3.5" one?
All the small ones are SMR these days, so that's something you should consider. Depending on exact use cases this may become very slow, and in case of error, like a sudden drop of power source which easily happens with externals, they also corrupt more easily (in other places, not just necessarily in the data you just wrote to them).
If you go for a bigger 3.5" drive go for a larger size and CMR. 4 TB is laughable and ultimately more expensive (EUR/$ per TB). I would recommend to look for 12TB and upwards with helium filled. The 18TB disks are the current price sweet spot it seems.