The best tool to create a bootable Windows 10 USB is to use the Windows 10 media creation tool. The benefit of the Media Creation Tool is that it downloads the latest ISO (32-bit or 64-bit) and writes the ISO to USB. Make sure you go to Control Panel and hit Windows Update to update Windows in general, but don’t upgrade to Windows 10 via the Windows Update, a lot of people have reported issues with this. https://www.microsoft.com/en-au/software-download/windows10
“If you need to install or reinstall Windows 10 using a USB or DVD, you can use the media creation tool below to create your own installation media with either a USB flash drive or a DVD. The tool provides file formats optimised for download speed and can be used to create ISO files.”
Some people report that the Windows 10 Media Creation Tool isn’t working or seeing something happened errors. I don’t think Microsoft is offering direct downloads of ISO’s via their website any longer, but if you can find an ISO of Windows 10 to download, you can use third party tools like this one below to write it to USB. Make sure your USB Drive isn’t locked via a hardware locking mechanism.