Who should I ask for my industry rec letter?

I'm applying to MS in ECE this upcoming cycle, and I want to include a letter of recommendation from one of my previous internships. I'm however conflicted on who should I ask as my recommender: 1, my actual supervisor who is the director of engineering; 2, my mentor who just got her PhD and joined the company when I was intern last year

My mentor was very helpful and responsive, and I worked with her the most on my project and learned a great deal thanks to her. On the other hand, my supervisor mainly just assigned me the tasks and discussed with me weekly in meetings. So personally I think my mentor might be able to speak for me and my work better, but I'm not sure if years of experience in the industry matter for grad application since my manager is on a much more senior position? Any advice is appreciated!