Use the 64-bit autoruns64.exe. In the end it doesn't really matter. You can also run the normal autoruns.exe and it should detect that you are on 64-bit and run the 64-bit one. CPU manufacturer doesn't matter.
The files with "c" in the name (e.g. autorunsc.exe) are for command line usage.
The files with "a" in the name are for ARM CPUs.