s/o of grills-what type of grates?

Cast iron definitely holds up better

Cast iron holds up better and holds temperature better for the cooking.

Cast iron.

Not what you asked, but I can't resist sharing this advice:
Make sure you buy from a reputable grill manufacturer, not just a well known name that's now been put on grills. My very expensive Jenn-air grill was cheaply made in China by a company that licensed the name.
Get one with burners that run from front to back rather than left to right so you can use as many or as few burners as you like. This makes doing indirect grilling a breeze.
If you can, you want any built in smoke box to be on the end of the grill, not in the center. When you're adding smoke, you want to be grilling over indirect heat and that means you probably won't have the center burners lit. If the smoke box is in the center, there won't be any heat to burn the chips.

Guess how I know these things?? Lol

Marcy