The way I normally make bootable USB drives in Ubuntu is with the dd command. It's worked well for me so far.
The last time I made a bootable USB was for Arch Linux about a month ago and I used:
Code:
sudo dd if=/path/to/your.iso of=/dev/sdx bs=4M status=progress oflag=sync
Where /path/to/your.iso is the path you your ISO file and /dev/sdx is the drive you want to use.