It's very hard to make a case for either of biochemistry or cell biology
over the other. Understanding the chemistry and enzymology without also
understanding how these mechanisms are used by cells tends one to ghastly
oversimplifications, which abound in the literature; but exactly the same
is true of understanding what cells do without understanding how they do
it. The best advice I can give is to major in whichever you find most
fulfilling but also to do plenty of courses in the other.
Aubrey de Grey