The Terms and Conditions state that you have to follow the Code of Conduct, so I daresay that makes Terms the higher priority.
"You must comply with the current version of any rules, guidelines, codes of conduct or instructions specified in any Jagex Product including our game rules, the current version of which is linked to here. The applicable game rules are expressly incorporated into these terms and conditions. Any use of a Jagex Product not in accordance with the game rules exceeds the scope of the license granted by these terms and conditions and is prohibited."
Agreed that the Terms and Conditions take priority over the CoC, especially due to the quote pointed out in Demither's post. The Code of Conduct are the official forum rules, but the T&C supersedes it.