Verified answer

Tough question. I have been in that situation. I was second highest on the seniority pole and got the promotion over the #1 person. It depends if they want to take the Extra responsibility on, etc. a promotion means changing your shift, hours and working with different people sometimes. I wanted it badly there was no doubt. I also deserved it though because I had the most experience and had 6 years if course work related to the job while the other guys only held a GED. Education makes a huge difference when comparing people. Some staff too, just are not motivated and would be bad leaders

It's not unethical. It might not be the wisest choice though, if used as the SOLE basis, although it should have some weight.