The example you use in this answer will help the interviewer to determine the level of responsibility you have in your current position. For instance, if your hardest decision is what to have for lunch, you likely aren't in a place to be the leader of 15 incumbents. Discuss some of the weightier responsibilities and decisions assigned to you, in your current or most recent role.
"The hardest decision I made recently was related to budget cuts. We had to eliminate some additional expenses but narrowing down which ones to cut was more challenging than I initially thought. I presented two options to my boss, and he is currently weighing the options I brought to him."
"I had to decide on which temporary associates to hire to cover the permanent employee vacation times this summer. I balanced between someone I knew would catch onto the job quickly but also fit in well with our clients and existing staff."
"The hardest decision I had to make recently was yesterday. I fired two of our lowest sales performers. These terminations came after some coaching opportunities were provided but not implemented. It is never fun to fire anyone, but this needs to be done at times to keep productivity and to reach corporate goals."
"I was recently asked by the owner of my agency to fire a client. It was a challenging situation because I do not like this type of conflict; however, it needed to happen. The client was not cooperating with the process needed to deliver our best product, and within their demanding timeline."
"The hardest decision I made recently was to create the employee schedule for the next week. My manager usually does the scheduling, but I was put in charge of this task while she is away on holidays. It's harder than I looks, but I believe I did an excellent job!"
"I had to swap around the client territory of our team last month. There were a few sales reps who were not happy about the change, but they were also the ones underperforming. I explained the system and also reminded them that the premium client accounts belong to the top performers."
"I recently recommended the suspension of a student with severe behavioral issues. It was not an easy choice; however, I had to evacuate the classroom a few times the past couple of months. This behavior is unfair to the other students."