I use portable drives from Western Digital for 3 years - first USB 2.0, Now USB 3.0. It is interesting to know that the copy on disk External USB 3.0 even by a port / USB 2.0 cable is significantly faster (Especially when there are a large number of small files) on a USB 2.0 drive. Obviously you need a port + 3.0 cable to operate 100% potential of your USB 3.0 drive. The difference can Shock You! On a 1TB disk, it turns backup times in minutes.
If you do not have the motherboard with ports USB 3.0 (it was my case), one can find an expansion card plus a front (very handy!), it's not expensive.
Similarly, I think that buying a USB 2.0 today is the mess (I made a comparison - it is the day and night ...). On Amazon, you will find key USB 3.0 cheap.