What is OBJ?

Wavefront OBJ is plain text, thirty-five years old, and readable by every 3D application in existence. Vertices, faces, texture coordinates and named groups, with materials kept in a separate .mtl file alongside - which is the part that most often goes missing when a model is shared.

What is GLB?

Binary glTF - a whole scene in one file, with geometry, materials and textures packed together. It's what web viewers, AR on phones and modern engines load, and it's designed to go from download to on-screen with almost no processing in between.