Polymaker PA6-GF Nylon Filament 2kg Grey Glass Fiber Nylon 3D Printing Filament - PolyMide PA6-GF Warp Free 3D Printer Filament

The most engineering-minded consumer brand in this space. Polylite is their everyday PLA, PolyMax adds impact resistance, and PolyWood nails the timber look. They publish data sheets and actually explain what's in their formulations.