Upload & Sell: Off
In my experience there is no significant difference in reliability or lifetime, but in terms of ease of use the USB powered drives make things simple.
Powered external drives are meant for desktop use and can be found with faster speeds, exspecialy those with firewire or e-sata. The USB powered drives are meant for portability and tend to run slower and are easier to carry offsite.
One thing to consider is application, extra storage (powered), backup (usb to take offsite), data transfer (usb).
For extra storage I have a NAS (Network Attached Storage) which allows both my Desktop and Laptop easy access. For my Desktop backup I use an on-line cloud service because it is a no brainer. For travel I use 2 usb drives to backup photos and keep them separated, 1 checked, 1 in carryon camera pack, and the laptop as personal item.
"Just because I'm paranoid, it does not mean someone is not out to get me."