Here's a pretty succinct article how to prep a USB key boot disk using diskpart
For wiping a drive and creating a single partition diskpart can be a lot faster than using a general purpose formatting program Gui.
The article shows the diskpart prep sequence. The remaining step is to put a bootable image on. Once the USB key is prepped it's usually a matter of xcopying the bootable files on with the correct switches.
The diskpart prep is very fast. The time consuming task is the format. I recommend using the standard format rather than quick esp. if the USB key is being changed from FAT32 to NTFS or vice versa. Better to have the entire capacity written in the format to avoid stuff grinding to a halt when you actually use it.
I mentioned this sequence a few times. Looking though Gizmo's site today I noticed this article. I was happy to see it didn't omit the clean
step in the sequence.