External drives are typically either hard drive disks (HDD) or solid-state drives (SSD). Solid-state drives are the best of the two options because they offer much faster performance. With no moving parts, they are also less prone to hard drive failure after getting bumped around. However, SSDs are more expensive.  If you are using the external drive for storing old files rather than actively working with those files, and if you are working at a desk where drops are unlikely, then an HDD will offer the most storage capacity for the price. For example, I use an SSD for files that I am actively working on, but I store past photo archives on HDDs, which aren't used often enough to warrant paying more for fast speeds.