I concede, dear Kommodus, yes indeed, Halberds are indeed the most versatile and dependable unit in the sense that they can take on anything to a certain extent. It's probably the best one can buy for it's money, for their cost is low, and in turn you get a highly armoured, very versatile (though a bit slow) unit.
In fact, in my army of choice, there would be a few of them, since they can fill the role of spear/polearm-men for defence against cav ánd defend against all kind of infantry, except the most elite of them. Still, I have an unexplained preference for Sword and axeman as shock troops, so where someone would bring Halberds, I would bring a mix of Halberds, sword/axemen and perhaps a few spear-bearing infantry or pikemen. For do not forget halberds are slow dudes, if the enemy has a lot of missile troops and some HA, it will be a drag to get to them in one piece. Because of their slow speed they are a bit difficult to use on the attack. My preference for sword/cav armies will probably be because I like to attack, and like it to be able to attack with speed.
Nevertheless, If you can take only a few troops, Halberds will be among them, mostcertainly on the defence and even on the attack I would rather not miss them. Superb troop type!