glTF (derivative short form of GL Transmission Format) is a file format for 3D scenes and models using the JSON standard. It is an API-neutral runtime asset delivery format developed by the Khronos Group 3D Formats Working Group. It was initially intended to be an efficient, interoperable format with minimum file size and runtime processing by apps.
Being called ‘JPEG of 3D’, GLTF is indeed a star of 3D model formats. Standard for many 3D applications and game engines, it is especially prominent as a common publishing format for 3D content tools and as the format of choice for web apps.
X3D is ISO standard XML-based file format for representing 3D computer graphics. X3D features extensions to VRML (e.g. CAD, geospatial, humanoid animation, NURBS etc.), the ability to encode the scene using an XML syntax as well as the Open Inventor-like syntax of VRML97, or binary formatting, and enhanced application programming interfaces (APIs). The X3D extension supports multi-stage and multi-texture rendering; it also supports shading with lightmap and normalmap. Starting in 2010, X3D has supported deferred rendering architecture. Now X3D can import SSAO, CSM and Realtime Environment Reflection/Lighting. The user can also use optimizations including BSP/QuadTree/OctTree or culling in the X3D scene.