What are the Pros and Cons to Using Photo Cells vs. Laser-Based and Infrared Sensors?

We're integrating an ambitious manufacturing line project that has us a little out of our depth for one element of it. We use proximity and other presence sensors on our machines all the time, but we're being asked to spec presence sensing to detect unauthorized personnel in the areas where all the machines will operate. First glance shows us many pros and cons among several technologies: the more conventional photo cells that we know something about, but also laser-based sensors and infrared sensors. We'd like to hear some best/worst practices or tips from readers about these two.
Send us you comments, suggestions or solutions for this problem. We'll include it in the July '12 issue. You can comment here or email us at controldesign@putman.net. Please include your company, location and title in the response.