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.
Current pfSense is 64-bit only, starting from version 2.4.
See also: Does pfSense support 64 bit systems