Usually, the best auto-rig tools for retopologized 3D models and weight painting include Mixamo, Blender’s built-in Auto-Rigger, and Adobe Character Animator.
Mixamo auto-rigs retopologized meshes and exports pre-adjusted weights compatible with most 3D software; Blender’s tool integrates seamlessly with its retopology and weight painting features for iterative tweaks; Adobe Character Animator uses AI to auto-rig and refine weights, ideal for linking retopologized models to live animation.
If you’re new, start with Blender’s free tools to practice combining rigging with manual weight adjustments, or use Mixamo for quick, web-based results with cleaned-up meshes.