>>1729851
The main advantage of a cast iron table vs. built-up steel is stiffness, stability, and reliable flatness. It's good for fabrication, hammering, etc. where more flexible steel tables might allow something to flex out of tolerance, or bow over time itself. Acorn tables and similar are widely used in industry, where their ability to take decades (or more than a century on some tables) of abuse while remaining flat is important. If the surface needs to be some other material (e.g. stainless steel fabrication, where cast iron contamination would nucleate corrosion), a plate can be affixed to the top of the table. A production shop may CNC-cut plates to match the hole patterns of their tables, so accessories like through clamps or holdfasts remain fully positionable.
As for which to get, it depends on what you expect to use it for. If you have an accurate understanding of the costs and benefits of each, go with what meets you needs better.