A grill is lined with ridges, which the food rests on top of as it is cooked. The oil and grease run down between the ridges. In certain types of grills, the grill surface is sloped, and the grease is collected in a pan.
A griddle is flat and can either be placed over a heat source or plugged into the wall. Food is cooked evenly on the smooth surface, and grease does not run off.
A grill is often associated with hamburgers and hot dogs. Typically, a grill is used outdoors to cook meat, leaving the infamous grill marks on meat. A griddle is used indoors and can be used to cook vegetables, pancakes or other foods made from batter.
A griddle does not provide much variety in type, while the grill has several different versions. Charcoal and barbecue grills are set up outside and cook food by using fire. Smaller indoor grills are powered by electricity on a counter top, such as a George Foreman Grill.
The best choice for you depends on your cooking needs. If you want to cook indoors and like using different foods, from vegetables to hamburger patties, choose the griddle. If you prefer cooking outdoors or like the taste of a finely grilled hamburger, a grill will better suit your needs.