A manufacture just asked me
For the USB interface , we have two communication protocols , one is USB to RS232 , one is USB to PS/2 .
Which one is faster? This is a USB Devise.
Originally, RS232 maxed out at 20kbps, but now it is 1.5 Mbps. PS/2 did not have a rate. It transmits serial data as 10-16 kHz, which means it probably tops out at about 20kbps.
RS232 is better (you do not need to reboot for it to be recognized) and faster.
http://www.datasheetcatalog.org/datasheet/SemtechCorp/mXryxtw.pdf