There is no single best site
Google autocomplete for this topic is “free PBR textures”, “Megascans alternative”, “Poliigon blender addon”, “Texture Haven”, and “CC0 textures”. Those are different jobs. Rank the job, not a winner.
Free CC0 first
ambientCG (people still type CC0 Textures) and Poly Haven (Texture Haven) are the correct first stop. HDRIs and models at Poly Haven. If the free map is good enough, stop. Matext is not a free-texture site. Details: /free-pbr-textures, /matext-vs-ambientcg, /matext-vs-poly-haven.
Blender shop vs Unreal scans vs archviz stills
Poliigon is textures + models + HDRIs in one Blender addon. Megascans on Fab is scanned nature for Unreal — Matext is not a forest library (/megascans-alternative). Arroway is the named parquet. Cosmos is usually already inside the V-Ray seat. Greyscalegorilla Plus is C4D look-dev. Substance Designer is authoring, not a shop (/substance-designer-alternative).
When you want a factory
Matext is photographed Organic, Logic seamless 2K / 4K / 8K PBR (wood, stone, marble), Torch, Studio briefs, and Atlas studio scans of a sample you send. Narrower catalog than Poliigon or Textures.com. When the SKU is missing, send a brief. Full tables: /best-pbr-texture-websites and /compare.