Better gas grills generally have two or more separate steel burners (not just control knobs) which allow greater control of the heat. Most lower-priced grills have only one burner shaped like an H or a bar, with one control or two controls. Be wary of "I" shaped burners as they tend to heat only down the center of the grill.
Gas Grills with one burner don't allow you to control heat as well as gas grills with multiple burners and may result in hot and cold spots on the cooking surface, however you can expect models with more burners to be more expensive. Side burners come in handy when heating sauces or side dishes in a pot or pan.
Note that stamped stainless steel burners will last longer than aluminized steel burners, cast iron longer than stamped steel, cast brass longer than cast iron, and cast stainless steel the longest of all. ABOUT TEMPERATURE CONTROLS
Separate controls tend to work best because they increase your control over the workspace and reduce the odds of your food getting burnt. Some of the better grills also have variable settings for each burner. This allows you to sear your steak on a high setting while grilling your fish on a low setting.
You can also find grills with settings for slow roasting (good for ribs) and regular roasting (good for cooking a turkey). An additional benefit of the gas grill is that you can clean the grate by briefly setting the burners on high after your food is removed. ABOUT BTU's (British Thermal Units)
Be aware that BTU's are not a measure of cooking power. They only indicate the volume of gas a grill can burn. Sometimes less is more: Tightly engineered grills can use fewer BTU's and cook food more efficiently, while too many BTU's can cause damage to burners and reduce the life of the grill. Generally, large grills with large cooking surfaces require higher BTU's. ABOUT CONSTRUCTION
Look for solid construction - A good, well-built gas grill will feel sturdy, while a poorly made gas grill will "wiggle". Choose a gas grill made of high-grade steel - these last the longest. The best cooking grates are either made of cast iron or stainless steel; some are also coated with porcelain enamel. A thicker, heavier-gauge cooking grate will last longer and distribute and retain heat better. Opt for a cart that is sturdy, with wheels that roll easily.