It depends. If they were battling, the Death Star would win. It's laser is far more powerful than any singular thing that the Star Forge would produce. If they ever opposed one another - considering it takes time for even a single ship to be built - The Death Star would wipe out the Star Forge with relative ease.
Having said that, an infinite fleet is more useful to me than a superstation capable of wiping out a planet. Sidious would probably think so to.