Mortgage vs Student Loan

Hello

Just a question really, it says on MSE to always pay your mortgage over your student loan due to the interest difference, but what if you have a 0% interest mortgage?

I'm lucky enough to have parents who have bought me a house (£160k) and I'm currently paying them back monthly (for 25 years, all sorted via solicitor) interest free. I also have a student loan of £28k to pay back. (Post 1998)

If I want to overpay, or I come into some money, what would be best to do? Overpay mortgage to parents? Pay towards my student loan? Put money into savings?

Thanks :D