First thing to decide is whether you want your out door stove to be hooked into your natural gas or whether you want to use propane canisters. The former is generally more expensive, especially when considering the cost of running the gas line. But.... you don't have to go back and forth for gas canisters.
Second thing to decide is what am I going to cook on this thing? If you haven't done that, how on earth could you ever know what you need?
Third thing to think about is heat control. You can't control the heat, you're hosed. And controlling heat isn't just about the burners. If it's cheaply made such that with the lid closed the heat goes out like crazy, you'll never get good heat control for anything that requires slower cooking like ribs or you'll have to (gasp) boil or oven bake them and just finish them out on the grill. But if all you're ever going to do is burgers and hot dogs you might not even care.
Fourth thing. Don't just fall for the one with the most BTUS. If you need that kind of power great. But if you don't, More BTUs=more fuel use That's more money on both types and more trips for canisters on your propane type.
Fifth. How portable do you need? Do you need one that fairly easily rolls away or are you just going to put it there and forget it?
sixth. Use a cover. Even if you plan to roll it into the garage during rainy season, use a cover. Your grill will last longer.
seventh. Ease of cleaning. Grills with a lot of nooks and crannies don't really clean easily. By the way, don't clean your grates where the food goes with wire bristle brushes. Those wire brushes can come off and stick, and get into your food and into you.
Non stick grates? ... Uh no.