Seasoning

• A cast iron grill rack needs to be seasoned before its first use, but a metal rack doesn't. To season, coat the cast iron rack with vegetable oil and fire up the grill, but don't cook anything. Allow it to reach as high a temperature as possible for at least 30 minutes. Let it cool.
  
  

Easy Cleanup

• Use a light coating of vegetable oil on the cast iron grill before each use for easier cleanup. A metal rack grill can be coated with non-stick cooking spray to make cleanup less of a hassle.
  
  

Cost

• Cast iron grills are among the most expensive grills available, but they last a very long time. A grill with a metal rack might be cheaper, but it isn't as durable.
  
  

Heat

• Cast iron holds the heat for a longer period of time than a metal rack. And the heat can be more evenly dispersed on a cast iron grill.
  
  

Weight

• Cast iron is heavy. A plain metal rack won't weigh nearly as much, making it more portable.