The trustee has a ______ duty to consider the best interests of the beneficiaries first in any decisions.

The correct term to fill in the blank is fiduciary. A fiduciary duty is a legal obligation that requires a trustee to act in the best interests of the beneficiaries of the trust. This duty encompasses loyalty, care, and good faith, meaning the trustee must prioritize the beneficiaries' interests above their own and make decisions that are in line with the beneficiaries' best interests.

In the context of trust law, the fiduciary relationship is fundamental because it establishes a level of trust and responsibility. The trustee is expected to manage the trust assets prudently and to make decisions based on what would benefit the beneficiaries, rather than acting out of self-interest or for any other motives.

The other options, while related to various legal obligations, do not encompass the specific nature of the responsibilities that a trustee has towards beneficiaries. A contractual duty refers to obligations arising from agreements between parties; a statutory duty is based on laws enacted by legislative bodies; and a discretionary duty involves decision-making powers but does not inherently include the requirement to prioritize another party's interests. Thus, fiduciary is the most appropriate and accurate term in this context.