Which would you choose? What determines your choice? I read articles stating that while USB sample and refresh rates are higher than ps/2, it may not be the perfect connection for a mouse, depending on what you looking for.

Is it true that if you are using high dpi optical mouse, you should always use a USB connection?

Until USB becomes more thoroughly integrated into the BIOS, I prefer having the PS/2 option. Right now I am using a wireless mouse that will go either USB or PS/2....

I personally prefer PS/2 keyboards and mice. I have yet to encouter a USB version that performs in a way that I would consider a significant improvement over PS/2.

With the possible demise of the PS/2 port with the introduction of the new BTX standard people like me are going to be very annoyed.

I prefer to not use the antiquated ISA bus, which is the bus used by legacy ports such as COM, parallel, and the PS/2 ports. Likewise, I have disabled all of those ports that I can. However, until we get rid of the need for the floppy drive (low-level & bootable apps still use the floppy) having a PS/2 keyboard is still useful.

I'm not so nostalgic about backwards compatability, so I personally can't wait to get rid of the legacy ports and the floppy drive (I don't have one) but first the software must die. Keep a PS/2 keyboard and put your mouse on whatever port you like. For now. ;)

And just for the record, I can navigate my BIOS just fine with a USB keyboard.

As for performance, it does not matter.
It depends on how man USB ports you have. If you have 4 or 6 you can usb without any problem. If you only have 2 I would not waste them one a keyboard or a mouse.

If you have the PS 2 ports why not use them?? Why tie up valuable USB ports when there are decicated ports for the keyboard and mouse that can't be used for anything else!
Besides you din't need software for a PS2 mouse and keyboard unless it is some 'special deluxe model with bells and whistles' that is a problem waiting to happen anyway.