By device do you mean hardware or peripheral?
If hardware: it's the CPU
If you mean peripheral it depends. It can either be your printer or your monitor, depending how big you want your monitor to be.
The most used input device on a computer is the keyboard.
A peripheral is a device that is connected to a computer. The most common peripheral device is a printer.
There are no records for the most expensive computer desk in the world. A computer desk price or value can be very expensive if it is a custom made piece of luxury furniture.
The most expensive computer is made in Japan. It is an Earth simulator costing over $400,000,000, which makes it the most expensive computer ever built.This very expensive computer is used for a variety of international projects. Most are related to atmospheric, climate, and oceanographic simulation.
The most used input device on a computer is the keyboard.
An output device is a computer device which receives the signal from the Micro Processors & gives the result to computer user. Computer Printer, Monitor and Speaker are examples of output device.
multiplexer
The Motherboard i think or maybe the processor.
supercomputers
According to TOP500, the fastest computer is currently (as of September 2017) the Sunway TaihuLight, at a speed of 93 petaflops. I don't know whether this is also the most expensive computer.
The most popular such device is the computer - the very device with which you asked that question, and with which I am answering it.
The most expensive Franklin Language Translator Computer will vary in price depending on where one is purchasing them from. In the United States the most expensive one's are around $200 and the cheapest about $15.