The best high-poly count for Unity 3D models depends on use case (main characters vs. background props) and target platform—desktop games often use 10,000–100,000 polys per asset, while mobile/VR typically needs 5,000–30,000 to avoid performance drops.
Unity uses real-time rendering, so higher polys increase GPU load—focus more polys on focal objects (like main characters) than background elements to balance detail and smooth frame rates.
If unsure, start with a mid-range count (e.g., 20k for a desktop character) and test in Unity’s Play Mode to adjust without hurting quality or speed.