I'd definitely prefer natsci to biochem (then again I'm probably biased as I really like the way the natsci course is structured).
Before I came to university, if you asked me what I thought I might like to specialise in I might have said biochemistry (though this may have been due to a lack of knowledge beyond a passing acquaintance with the other fields of biology).
After the first two years (as a medic; but the same principle of flexibility applies), having learnt bits of anatomy, biochemistry, physiology, pathology, pharmacology, neurobiology and reproduction, I decided that though biochemistry was still interesting, I was far more interested in pathology.
Am now doing my third year in pathology - and it's an aspect of biology that didn't even cross my mind three years ago when I was applying for university!