My old Baneblade only ever saw one game but it did very well there, killing about 400pts worth of models by itself and surviving the game, albeit a bit beaten up.
The Hellhammer and Stormsword are like Eradicators on Steroids. Their main guns, although short ranged, will kill just about anything they hit regardless of cover. And although they are short ranged, they still shoot further than a Demolisher Cannon. They're definitely weapons you can use to control the board and ward off Infiltrators and Scouts with.
In 'smaller' games I'd take a hammer or sword over a blade in order to control a chunk of a table. Out of the two, I'd probably take a hammer. The turret makes the gun more useful, even if its one not quite as good as the sword's.
Having said that, Baneblades are still great. I'd use them as crowd control, because they pack two big blast templates and multiple heavy bolters. Unless they're cover, it should wipe out a unit a turn.