Here are our top four picks, plus three other contenders you'll want to consider.
Seagate Backup Plus Fast (4TB mechanical; RAID 0, USB 3.0)
Seagate's Backup Plus Fast is loaded with great features, including an attractive price-per-gigabtye of $0.07 (you get 4TB of capacity for $270). And because this is actually two mechanical hard drives operating in RAID 0, you get phenomenal speed. There is a downside to RAID 0, however: If one drive fails, you'll lose all the data on both drives.The other downside of having two drives in one enclosure is bulk: The Backup Plus Fast is nearly 0.88 inches thick, and it weighs 10.9 ounces. That's still a tolerable weight, though, and it's comfortable to hold in your hand.
Adata DashDrive HV620 (2TB mechanical; USB 3.0)
Adata's DashDrive HV620 is a good drive, with a big chunk of storage capacity and a great price per gigabyte: $0.07. It's a good choice for anybody looking to maximize their storage on the go without breaking the bank. It's not nearly as fast as Seagate's Backup Plus Fast, because it's not two drives operating in RAID 0, but neither does it come with the tradeoffs of that arrangement. The HV620 is a plain and simple portable hard drive, and a very good value.
Western Digital Passport Slim (1TB mechanical; USB 3.0)
This drive won't take a lot of space in your laptop bag, but it delivers a full terabyte of storage for taking your data on the road (a 2TB model is also available). The WD Passport Slim also makes a fine backup drive for home-office duty, either plugged into your PC or shared over a network via the USB port on your router. WD provides backup software for automated backups (you can also back up to a Dropbox account) and security software so you can password-protect your data. It costs $0.65 per gigabyte.
Apricorn Aegis Portable 3.0 (256GB SSD; USB 3.0)
If speed is your primary need, Apricorn's Aegis Portable 3.0 is our favorite portable SSD. But be prepared to pay for its performance. While it's come down in price since it was first introduced, you'll still pay $1.09 per gigabyte for this 256GB drive. There are less-expensive portable SSDs on the market, but few that match the Aegis Portable 3.0's outstanding price-to-performance ratio. This isn't the best choice for a backup solution, but it's just the ticket when you need to transfer files rapidly.
Other strong contenders
Elgato Thunderbolt Drive+ (512GB SSD; USB 3.0, Thunderbolt)
If you absolutely need the compelling speed that an SSD paired with a Thunderbolt interface can deliver (and have a Thunderbolt interface on your PC to support it) Elgato's Thunderbolt Drive+ is the fastest — and most expensive — portable Thunderbolt drive we've tested.
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