What's your price range? What will you use it for?
The market is very dynamic, reacting quickly to consumer prejudices. However, most consumers are not well informed as to what does and doesn't make a good grill and are often deceived into big-ticket purchases by a few "buzz word" features. "304 Stainless Steel," and "infra-red" are no longer guarantees of quality. A great number of grill "manufacturers" assemble their grills completely from generic parts purchased from China. Many "manufacturers" license their names to real manufacturers who turn out grills under a variety of names. These sorts of grills include some luxury stove company names as well as big box (Home Depot, Lowes, etc.) sellers' house names. Those are the grills best avoided.
The number of burners in a grill, is a function of the grll's dimensions, and of how the burners are oriented. Since burners are almost always oriented front to back, rather than side to side, width is the usual determinant. Some very good grills use proprietary burners.
It's possible to do indirect cooking in a propane grill, but difficult to do a good job. The reason is not the fuel, but the relatively confined dimensions which require to close a proximity of the burner to the food. Also, gas grills tend to be rather drafty. With a little thought, and a little extra trouble, a gas grill can be an adequate smoker. But won't compete with a $200 Weber Smokey Mountain.
The most common grate surfaces are chromed steel wire; porcelain over steel; porcelain over iron; cast iron; and, stainless steel.
Chromed steel is always made using heavy gauge wire. An example is a Weber (charcoal) Kettle grate. This type of grate is usually confined to the least expensive gas grills. They are difficult to keep clean, bend easily, and are generally not as good as the alternatives.
As you already know, porcelain chips -- and having begun to chip, deteriorates quickly. Porcelain grates are relatively easy to clean, resistant to corrosion and (typically) made with a substrate that cooks well.
One doesn't find quality cast iron very often in gas grills. Although they are good performers, they require lots of maintenance to avoid corrosion. They are almost, if not just as expensive as stainless. I've used cast iron cooking grates for years in charcoal and gas grills, and would not recommend it for gas -- except for the exceptional user.
Stainless steel is the current up-market favorite for cooking grates. If you can afford it, it's your best choice. Grates can be made from round, square, or rectangular bar stock; or round, square or rectangular tubing. It doesn't make much of a difference to the cook, as long as the grate is strong and well made. You don't need to be an expert to tell by look and feel. Remove the grate, heft it, tweak the bars, look at the welds -- you'll know.
Everyone wants those sexy grill marks tattooed on their food. The key is a pre-heated, clean grate. Stainless is good because it cleans so easily and can stand up to vigorous cleaning. The primary benefit of cast iron -- seasoning -- does not come into play at all, because the grates must be cleaned so often. I clean and oil the cast iron grates on my charcoal grill (Bar B Chef Texas Charcoal) after and before every use. Stainless, I only clean and oil before.
You'll have to decide for yourself if you're going to do enough rotisserie cooking to justify a rotisserie burner across the back of the grill. If you eat a lot of steak, I'd highly recommend purchasing a grill with an "infra-red" a k a "sear" burner. Write back with more information, and we can get into it a little more deeply.
Weber does not make the best gas grill for everyone. But they do make a good grill, sell it for an honest price, maintain a parts inventory for decades after model changes, and a helpful "help line." Weber = safe choice. Sears "Craftsman" grills are also good value for money. But, again, if you want to explore some of the less common brands like Cal Flame, or Napoleon, or the big-ticket faves like Viking and Kalamazoo, write back and let us know.
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