Stats or Decision?

I honestly have no idea which would be best for me. I'm doing Biology, Chemistry and Physics and hopefully want to do either Medicine or a Physics degree at uni.

The courses are:
Decision - Decision 1 in year 12, Mechanics 1 in year 13
Stats - Stats 1 in year 12, Stats 2 in year 13

or there's a small chance I could do S1 them M1 but it's not guaranteed.
Help!

So basically
Decision sucks
Stats is ok
Mechanics is the best

But I'll just have to get over decision if I really want mechanics?