I've been meaning to pick up an external hard drive and I'm wondering about what I should get. Should I get USB or SATA? What is the difference? I know you can pick up USB hard drives that don't require a separate power connector, is it the same for SATA drives?

USB only are normally 2.5" drives uses power from your computer. If it says external SATA it means you can connect it to your external SATA socket at back of PC (if you have one - i know many older ones do not come with that socket). SATA ones usually have an external power supply and 3.5" drive inside. There's pro's and con's for bother...

Right ok, so SATA drives have an external power source, thanks!
If I'm looking for speed, which would be preferable?

external SATA is always faster, but not sure how it compares to USB3.0 drives. might have to google it.. too sleepy to look lol

Most drives available to buy are USB. The 2.5" ones don't require extra power. If your intention is to have something portable which you can move between PC's, then USB is definitely the way to go.

Absolutely a key point.

I'm looking at a 1.0 - 1.5TB USB portable since my old gOg backup drive gave me the "I'm FULL" message last night. It'll be a USB 3 model as the laptop doesn't have an eSATA port, and neither does our desktop.