Stainless vs Enameled Porcelain Grates?
Prefer the larger, heavier grill.  It's about thermal capacity and grill marks.  You want the grill itself to be hot so that when the meat touches it, it immediately sears the meat on contact.  The bigger the thermal mass, the better this works.

Regardless of what you get, you're going to need to replace the grates every few years, so bear that cost factor in mind.