your bloodhound can track and find your kills. That's extremely helpful.
This. It's a pain when there isn't a mini map marker and there a dozen corpses scattered on both sides of the road, in the grass and the trees and down the slope…
I don't have wide experience with other devs, but I love how Ubi do their wildlife—truly excellent.
Nice for a photo, and occasionally otherwise, but mostly a pain when they're near where you're looting and you have to focus on whether the E key shows 'Pet' or 'Loot' or 'Swap weapon'—but of course that's a commentary on abysmal UI design, not on pets. Sorry, grr, meow, woof.
What kind of functionality should the pet have to be fun
'Fun' gets old pretty quick for me—I mean the cutesy stuff built-in—so for me, fun mostly = useful.
Locating kills as you said, and the other big one is reviving me when I'm dying. What I haven't seen which would be great is doing all the nearby looting! Boomer in FC 5 can get you extra with one of his upgrades, but not do the basic loot.
The Owl in FC Primal is a neat tagging system, but they should have made it possible to fly on-high like an AWACS—or provide a hawk for that
A QoL thing would be to have them stay 5+ meters away from you when possible—as you say, getting underfoot gets to be a real low-level constant pain, to the degree I often play without buddies.