Building your own atuo-rigger is good, and it shows technical competence. However, they’re readily available, and most studios will have their own already. It’s worth showing, but IMO the most important thing is deformation.
Show some extreme body poses. Arms-over-the-head afraid (shows off shoulder deformation), bend him backwards over a chair (show off spine deformation), do the splits (the hips this time). Show some more extreme facial poses too, like suave, scared, petulant, leering, rage, or laughter. Showing complicated controls is fine for a bit, but rigging is about enabling animation, so I want you to show me that your rig would enable an animator to hit the poses they want.
The best way to show this is, of course, to show a rig actually animated. Animators have a tendency to make rigs do … shall we say “unexpected” things, and it shows you can deal with anim requests. If you can’t get that (it can be difficult early on) and you’re not so much of an animator (like me!), then find some strong poses from a movie and copy them. You may not be an animator, but you need to at least recognize good silhouette, because you’re in control of that. You want to try to match some insane silhouettes, try Cloudy, or Hotel T.