Which hard drive are we talking about here, 3.5" or 2.5"?
One big advantage of the
Seagate Backup Plus hard drives is that you can pop off the USB adapter and replace it in 5 seconds. Lots of people complain about failed enclosures rather than the hard drives themselves - this fixes the problem.
You can also replace the USB 3.0 adapter with one featuring
FireWire 800 (probably useless in 2014) and
Thunderbolt (overkill for a hard drive and only one port). All those adapters work with other SATA drives as well - they just have a standard SATA connector.
Western Digital on the other hand has the
MyBook Ultra, which has automatic cloud backup that doesn't work on a Mac, and "Turbo drivers" of which everybody who had installed them wasn't too fond of.
From a Mac user's point of view, the 7200RPM 2.5" hard drive crown might very well go to the
Seagate Backup Plus - easily replaceable "enclosure logic", no weird drivers, no nonsense.
If you want a slim hard drive:
WD MyBook Air or
Seagate Slim - pick one.
The inexpensive 5400RPM option?
WD Elements or
Seagate Expansion - pick one.
Or build your own, or upload your data to the cloud, or create your own cloud with a NAS. Unlimited possibilities.