I own several external 2.5'' HDDs on the 1 TB range where I save my data. Samsung has worked well for me, but now I need more space.
One option would be to buy an external SSD instead of HDD.
Another would be to get an external NVME, but so far I haven't found cases for them.
Nowadays we even have 1 TB flash drives, should I get one of these instead?
I could also buy 2 0.5 TB micro SD cards instead.
So many options make it difficult to decide.
What brands and technologies do you recommend?
Software is going to be debian based.
Be careful if you buy a Samsung 8x0 SSD. They have long standing bugs that may cause data loss. They are worked around in the kernel, however you have to ensure that the workaround for your particular model exists in the kernel version you use.