Recommendation from a senior member of organisation

Hi everyone,

The Tech Nation guidelines indicate that the letters of recommendation need to be from senior members of an organisation. I am currently faced with a dilemma:

I can either request a recommendation letter from my University supervisor who used to be a lecturer and now he is out of academia working in the industry as a mid-level Data Scientist (so not a senior member of the organisation he is currently at).

Or I can request a letter from the Head of the Economics Department of the same University who is still in academia.

The thing is that my supervisor knows me a lot better than the Head of the department (even though the head of the department wrote a letter of reference for me once when I was applying to an MSc degree).

Would my application be rejected on the technical grounds if I request the letter from the supervisor? Who would you suggest choosing as my referrer to increase the chances of having a successful application?

Thank you!