Precision T5810 which USB port should I use to boot from bootable USB stick

My Precision T5810 has two USB 2.0 ports and 4 USB 3.0 ports at the back and a further 3 USB 2.0 and one USB 3.0 ports at the front. (these are controlled by 2x Intel C610 series/X99 chipset USB enhancedhost controllers for the USB 2.0 ports and Intel USB 3.0 extensible host controller for the 3.0 ports)

I have the option to boot from a USB storage device, e.g. from the boot once ( ) menu. Which of the USB ports should I use if wanting to boot from USB bootable flash drive (USB stick)?

One example for which I might wish to do this is to update the BIOS using a DOS-bootable USB flash drive. instead of doing so using Windows system method.