Core 13.0 is the base for the enterprise version. Core 13.3 was released for the community so that people could update their jails and some fixes with bhyve for vms. Core is now in kind of a long term support status, it’s still usable but won’t get any updates anymore (apart from security and maybe minor bug fixes).
Scale is the version that’s in active development and get’s new features like recently zfs expansion, which is not available on core and propably never will be. Scale get’s 2 major releases a year, one in april, one in october with minor point releases in-between.
If all you need is SMB access there’s no need to update to scale any time soon, but some day you might have to migrate to scale if iX decides that core won’t get any more security fixes. Or you want to start to play around with apps or want a zfs feature that’s only available on scale.
The choice is yours.