You have chosen the number of burners you need, however, you also need to determine the burner material. Looking to keep your grill for awhile once you buy? Keep in mind this order of longevity. Aluminized steel burners have the shortest grill life. Stamped steel is next followed by cast iron, then cast brass with cast stainless steel the best option for long life. Most of today's grills have these steel burners.
Note that typical two burner grills should form an "H" rather than an "I", as the "H" shape is going to give you better heat spread rather than the center of the grill heat source provided by the "I" shape.
Having a side burner is a handy option for cooking vegetables or sauces without leaving your grill location but will bump up the grill cost.