Meat and Eggs can be classified into three different types, based on the effect they give you upon use. The first type is Egg Dishes. They typically offer some Hit Points and Magic Points, with omelettes offering additional stat bonuses. The second type, Amphibian Dishes, offers Dexterity and Attack (from which Thieves are most likely to benefit). Egg and Amphibian dishes typically last either 30 or 180 minutes.
The third type is Meat Dishes, which all offer Strength and Attack and therefore are the most popular with melee and Ranger jobs. There are two relatively distinct subcategories of meat dishes, Finger Food and Meals. Finger Foods are the smaller dishes (dried, skewered, smoked, etc.); most of which stack, last for 30 minutes. The larger Meals (broiled, grilled, sauteed, etc.) do not stack, last 180+ minutes, and a majority offer a wide-range of stats. Since some meals tend to be costly, one should decide wisely what works best for what and where.