I have both. I have the PED Basic for my smaller machine, which does not have a USB port. What I liked about the PED is you can set it for the design size you need, like 4x4, and it will not allow you to download any designs that do not meet that criteria.
The USB doesn't have that feature so when you download a design from your computer, you need to know if it will fit your 4x4 size before you download it. I use the USB on my bigger machine because I can accommodate all hoop sizes so it's not an issue.
PED is limited on the number of designs that will fit on the card. The bigger the design, the more space it will take up on the card. The USB can accommodate tons of designs, all sizes.