Disassemble raw x64 machine code

And as usual writing down the question already gives you some rather good ideas what else to try..

Anyhow the right machine architecture is: i386:x86-64.

The full command is:

objdump -b binary -D -m i386:x86-64 <file>

If you want to disassemble code that expects to be loaded at a specific address, you can add the --adjust-vma <load-address> flag.