It’s a really dangerous rabbit hole to go down when you start thinking about which degree will give you the ‘best chance to get into Med’ without asking more nuanced questions that pull that notion apart.
The best degree for you is one that you’re interested in. You’re more likely to apply yourself to the course, complete assignments to a high standard etc. There’s literally no degree that correlates meaningfully with a higher chance of getting into Med. If you look at graduate entry, the successful students are heavily skewed to BMedSci-like courses, but that’s very much due to sheer numbers. The proportion doing those degrees SPECIFICALLY to get into Med is massive. This makes them stressful, competitive, and incredibly over subscribed. And also means those missing out on grad Med ALSO skew heavily to BMedSci students.
If an alternative back up career for you is medical research of some kind, and you’re prepared to need to complete a PhD, then that’s a completely fine option to take, but if you’re choosing it ONLY as a stepping stone to Med, then literally any other degree will serve you just as well (and probably better). Alternatively, if you think you could see yourself using a BMedSci to move into a professional masters (examples: dietetics, physio, speech path, a gazillion others...), then that’s also decent use of a BMedSci-type degree.
But I think the first step for you is to consider a shift in the way you ask yourself those initial questions.