I'm getting a bit tired of RuneScape and if I don't play again, I want to know I accomplished something, so I want a 99.
Cooking, using lobsters, would cost me 6,054,788gp using today's prices. I'd buy raw and sell cooked.
Firemaking, using Maples, would cost me 3,820,446 using today's prices.
Cooking is easier, but Firemaking is cheaper. If I got cooking I'd need to make about 1.5m more.