Be sure to take some print/copy samples with you when you leave the demonstration. Mark the manufacturer/model name on the samples and bring them with you when you go to the next vendor's demonstration. The best way to assess image quality is to do a side-by-side comparison.
Since the machine in question will be expected to run high volumes, you'll want to make sure that operators will be able to set up and run their jobs with as little manual intervention as possible. This ensures staff can be more productive by performing other tasks while the machine is operating. Be sure that the document feeder can accommodate enough originals so that the operator doesn't have to split jobs. The standard for a high-volume device is 100 sheets. Feeder speed should match rated output speed.