I'd personally try to approach this from another angle: what problem are you trying to solve?
I suppose you roughly have the choice of two or three loaders. Sort off. One for MBR partition schemes and one for GPT. And then there's one for UFS based installations and one for ZFS. And finally there's also Grub from the ports collection.
Oh, and I almost forgot about, I believe, boot0 which can be used as a boot menu (typing this from mind). Problem is that not every boot loader will be usable, depending on your environment.
I have quite a number of 2.5" disks most of which came with some version of Windows installed. I've installed various versions of Linux on some and FreeBSD on a lot of them after reducing the Windows partition and am looking at the best way of using different OSes on them.
I installed Arch Linux on one which also had FreeBSD installed, but I couldn't get Linux's Grub to add FreeBSD to its menu. Eventually I installed FreeBSD's Grub and can boot FreeBSD, but can't figure out the Menuentry for Arch Linux.