Most useful - Magic, Fishing/Cooking combo. Think of how many things magic can do for you. From teles, to combat magic to battle, to spells to help with crafting. This skill can do it all. Fishing because I believe it supplies atleast 90% of the food used during combat in one way or another and who doesn't enjoy combat every now and then? Least useful - Firemaking. Although I eventually plan to get 99 cause the emote rocks, it doesn't have many in game uses these days.