USB 3 drives have several potential issues:
-some models give issues when you try to format as bootable.
-some have propietary partitions that can persist formats
-many laptops/netbooks will boot USB's at 2.0 speeds, even if it's USB3 port with USB3 drive. Go figure.

Thus I recommend USB2 for Live, bootable install.  It's the most cross-compatible and reliable platform IMO.