Doing another degree just to get into medicine? TSR will judge you.
As a practical answer, MPharm gives you greater eligibility for more GEM courses and sets you up better for the GAMSAT. However, for courses that say they don’t care which course you do, there’s really no advantage either way.
I think it’s conceivable that you may end up doing either career long term. If this is the route you’re taking, do whichever one you think you can stand doing for the longest.