I am seeking your advice on a tough decision I need to make.

I have two highly dedicated team members who are both up for a promotion this year. However, HR has informed me that there’s only one promotion available. Here’s my dilemma: One candidate has 3 years more seniority and consistently delivers excellent work when assigned tasks, though he tends to be more reserved and doesn’t voice concerns. The other candidate is newer but a quick learner who shows great initiative. She’s very vocal, enjoys training others, and is always looking for ways to improve processes. I’m struggling with this decision because promoting one over the other might be discouraging. Any advice on how to handle this situation?