Knock out 99 Cooking.. 145k exp/h at 68 cooking.. It takes around 3-5 days for 99. After that, go for a more respected cape. 99 Thieving/Agility are always a good pick.
If you have the $, go for 99 Construction too
99 Farming. Its one of the rarest capes and if you have money it is quick (I'm assuming you have a lot of money since you have 99 mining.) Oh and the Skillcape looks amazing