Med is harder imo.
I say this not because It's my choice of career but because of alot of reasons...
Ok, first of all there are just so much more processes to even get to the offer stage. Take the fact that you need to apply for UMAT fairly early in the year and then the individual uni application processes which will ask you questions that often require a genuine reason for pursuing medicine that, trust me, is harder than it sounds (stopping any students who decide to do medicine at a whim).
Let's not forget that the interview is a difficult situation that requires alot more preparation and knowledge of yourself and your wants than you would think. It's a big deal and you utilises skills that, like UMAT and unlike the HSC, are difficult to simply practice.
To be competitive you need a high UMAT and a high ATAR. Though you can get into interviews for med with an ATAR less than Combined Law for places like UWS, Newcastle and Monash as they focus very very heavily on UMAT, achieving a high UMAT is, imo, much much harder than attaining a high ATAR. Why? because you have to think the way they want you to think and be naturally gifted. This is unlike your subjects for HSC where you can take almost anyone with half a brain and train them to get 99+ so long as they have determination.
At uni's like UNSW you want to have an ATAR of at least 99+ to be competitive and for UQ you need 99+ to be eligible for provisional med entry.
As for Combined Law, anyone can simply decide at the end of the year to enrol in it because they got a high ATAR (i think i've made it clear that i think a high ATAR is no where near as problematic as trying to achieve a very solid ATAR, a solid UMAT and a solid Interview) and I have seen this first hand with some people who have exhibited no interest in law or commerce in their entire schooling careers whatsoever but then decide to do Comm Law simply because they get a good ATAR and decide to not "waste" their marks... you couldn't pass a med interview with an attitude like that.
Anyways, if you can't get into Comm Law first time round, just do commerce for a year (need only ~95) and achieve a good average (i think 70+ for a uni?) and transfer into Comm Law. This is VERY easy compared to transferring into medicine after a year as you need not only a good average but also need a good umat and good interview. So if we take the alternate pathway criteria for entering Combined Law/Medicine, Medicine is clearly the much much harder course to get into.
That being said, I'm sure there are some people out there that could breeze through UMAT and interview while have trouble achieving a high ATAR simply because of poor work ethic or less fortunate situation with tuition/schooling as others.
There are probably many other points to consider both ways but that is how I see it.
