Many people want to know whether to buy or use a PS/2 or a USB keyboard .so please consider following factors before buy your new keyboard.

Convenience
The USB interface supports hot swapping meaning you can disconnect and reconnect devices while the system is powered on. The PS/2 connector does not technically support hot swapping, if you connect or disconnect a PS/2 device you may be forced to reboot. That said, most newer computers are tolerant of this and continue to work. But even so there are sometimes issues.

Another benefit to the USB connector is it is easier to connect when you can not see the plug (reaching around behind a computer). The PS/2 connector being round is harder to connect without bending the pins. Also, many computers have USB connectors on the front for convenience.

USB Allows for multiple keyboards at one time
This is convenient for keyboard co-op games or if you just like having multiple keyboards to swap for different tasks (gaming versus typing)


PS/2 implemented poorly on many modern motherboards

Availabilty of Keyboards
Quite simply it is getting harder and harder to FIND a PS/2 keyboard as Logitech/Microsoft/HP/Dell move to exclusively USB keyboards. And if you want a Realforce, a Happy Hacking, or a Razer Mechanical there IS no PS/2 choice or ability to work with a simple purple PS/2 adapter

Resale Value
USB keyboards are more popular and therefore easier to sell. Unless you have a IBM M15 of course.


source:[geekhack.org]