Everyone pushes their own lab results. Real-world performance is about resource impact on endpoints and admin overhead.
I've seen both in production. GravityZone is lighter on the endpoint, which is its main selling point. Trend Micro can be a resource hog, especially during full scans, which forces you to schedule them carefully. Their rootkit scanning is particularly aggressive.
But the hidden cost with Bitdefender is the portal. It's slow, especially for a global tenant. API is decent, but the console lag adds real time to your workflow. Trend Micro's management console is generally more responsive.
For TCO, don't just look at the seat license. Consider the admin hours lost to a sluggish interface and the infrastructure needed to support a heavier agent. Neither is perfect, but the performance question depends on what you value more: endpoint CPU or your own time.