Bluetooth is a global open wireless technology standard for exchanging data over short distances (using short wavelength radio transmissions) from fixed and mobile devices, creating personal area networks (PANs) with high levels of security.
USB is an acronym for Universal Serial Bus, a standard for a serial host-to-device protocol defined by the USB Implementors Forum.
Commands useful slower
|Connection sometimes easier||
"It depends on your requirements but setting up a usb connection is sometimes easier than managing a bluetooth connection"
from question "Serial communication with Windows Phone 8"
"I had previously sent those commands via bluetooth but the connection fails too often to be useful and is slower than usb"
from question "How to use Visual Basic, Mindstorms NXT and USB communication Altogether?"
|Connection far more reliable||
"On the other hand a usb connection is far more reliable better supported and of course has the inherent advantage of speed and since it is well supported does not suffer from all the pitfalls bluetooth connectivity does"
from question "Android + Arduino project: should I have them talk via Bluetooth or USB?"
"Interfacing with usb is more difficult than it sounds it would be harder to build something which would interface with that and measure millivolts than with bluetooth because the pic processor you use for analog to digital sampling and usb client would in fact have to either act as usb host or usb otg on a phone which is far more complicated than being a usb peripheral"
from question "Reading milliVolts in Android for pH Tester"
"If your watch doesn t have usb support moto 360 and other induction only charging you need to enable bluetooth debugging slower than through usb though"
from question "Android wear Watch face installs but not shown in faces list"