Pi-hole is a little easier for someone who's not into networking to deploy. I would give a beginner Pi-hole much sooner than I would introduce them to OPNsense. (I run both, OPNsense for my studio network, and Pi-hole + Asuswrt-merlin for my homelab)
I installed pihole once. Not a fan. Since then I've been using Adguard Home. It's a single go binary so it would work fine on pfsense/opnsense either directly or in a jail.