I just ran the numbers on this, looking at Temple Guard fighting different types of Dwarfs, but the results should be applicable to other rathers.
Basically, if you get charged by hard-hitting units like Hammerers or Slayers, it pays to put up the shield wall. Against less hitty units, say ones putting out 5xS3 or 5xS4 attacks, the halberds are better, at least if the opponents are armored.
The Halberds are also better in nearly every case where you have the charge. The possible exception would be Unbreakable or Stubborn units. Stubborn, save 5+ great-weapon wielders like Hammerers are probably best dealt with using Halberds, but in fighting unarmored Slayers, the shields and hand weapons provide long-term survivability.