2D Tables: These are traditional flat, planar surfaces, often just a plate of steel. They are simpler, more affordable, and suitable for general welding, but are harder to expand and are generally not as flat or strong.
3D Tables: These are newer designs that feature a flat top plus sidewalls, all with fixture holes. This design makes them significantly stronger (up to 30 times), an order of magnitude flatter, and highly modular. You can bolt accessories, extensions, or even other tables to the sidewalls.