Although you seem really smart, try not to overload on subjects, come exam time it might just all pile up and you wont know what you just got hit in the face with..
If you can handle it though i don't see a reason why not.
I vote biology cause its awesome.
I picked biology on a whim, didn't even think i would like it, now i love it.
I'm not sure how this happens (its not even that hard of a subject) but at my school most of the people i've asked get abysmal marks in biology (or maybe they dont care cause its not going to be their top 4) so the competition isnt very strong at all.
Do you really find that biology that much work? I pretty much just showed up to class did homework and a little study before the exam and killed 1/2.
(hopefully this makes some kind of sense its 1am and im tired..)