To the best of my knowledge and reading many insightful posts here, magnetic HDD have a higher chance preserving data if stored in good conditions (no water or humidity, far from magnetic fields, …). SSDs as I was told need to be powered in order to preserve data begging the question about the usefulness of external SSDs.

There are full sized external drives that have their own power supply. I think they are basically the internal ones with SATA to USB adapter inside an enclosure.