Different purposes
COLLADA is XML-based interchange. FBX is common in game and animation pipelines but behavior varies by application and FBX version.
Geometry is safest
Vertices and polygons are usually most portable. WebFixKit supports triangles and polygon lists. Convert modifiers, NURBS, and procedural objects to ordinary meshes first.
UVs and materials
A first UV set may transfer. Image files are separate and node materials rarely map one-to-one, so expect to reconnect textures and rebuild shaders.
Rigs and animation
Skeletons, weights, curves, constraints, and morph targets require full DCC conversion and are not supported locally.
Scale and axes
A unit can mean a meter in one tool and a centimeter in another. Up axes differ. Validate with a known dimension, inspect normals, test UVs, and archive the original.