Is 32-bit or 64-bit pfSense Preferred
If hardware is capable of running a 64-bit operating system, always use 64-bit versions of pfSense.
Though it is technically possible to run 32-bit (x86, i386) versions of pfSense on 64-bit (amd64, x86-64) hardware, this is not recommended. Always use 64-bit versions pfSense on 64-bit platforms.
In the past, the amd64 version of pfSense was new and not as well tested, but the situation has changed over time. The amd64 version has matured and is now more widely used than i386 for new deployments.
See also: Does pfSense support 64 bit systems