University

Here's your second opinion:

Don't do a degree with the sole intention of using it to apply to GEM.

It's not a case of just getting a degree and then just getting accepted to GEM. GEM should be for people who have a degree, and have now decided they want to do medicine. If you don't get the grades, take a gap year, resit, get some work experience, and re-apply. If you get the grades, but don't get a place then take a gap year, use it productively, and re-apply the following year.

Neither of those degrees will be "better" for a GEM application. I understand you feel like your original question is not being answered, but that's because the question itself is rooted in what appears to be a lack of understanding about the best way to get into medical school. You're in a stronger position to get into medical school as a school leaver with good A-levels (even if they're resits) than as a graduate.

Hope this helps!