Yah... I agree that physics and chem will give you more choices
when you decide what course to take in university. If you don't
take A-level bio, you can always take introductory biology in
university. (In NUS, you can take this module "General Biology" and
use it as a substitute of A-level bio. IMO, this module is much
easier and less time-consuming than A-level bio.) I dun have
A-level bio, so I took "General Biology" in NUS. After that, I took
modules in biochem, molecular bio, medicinal chem, etc, and I'm
doing pretty well. This shows that A-level bio is not really
necessary if you wanna take bio-related modules in university. Of
course, some courses in NUS, like pharmacy and food science &
technology, requires A-level bio. But most other courses do not
require A-level bio. If you still have no idea what courses to take
in university, go for A-level physics. It's more useful.
As for the contrasting subject, most people would go for econs.
Econs may be the most relevant and useful to real-life situations,
but it's rather tough and hard to score. Humanities are not that
easy either, as you need to write fluent essays most of the time.
As for me, I chose something special. I chose A-level art! I like
A-level art, because I dun need to go for boring lectures. Class
size for art is normally small, meaning that there're more
interactions between the teacher and students. While my classmates
are furiously writing econs essays, I'm happily drawing pictures.
Of course, A-level art can be pretty "siong", esp when I have to
rush my A-level art project. Also, art is something that I have to
keep practising. (If you don't have the talent, you may need to put
in extra effort to polish your drawing skills.)
If you love drawing or designing, and if your JC happens to offer
A-level art, you can give it a try! If you dun like it, you can
always change subject after 3 months. Hehe. 
You
can also check whether your JC offers music, or mother-tongue
language & literature (e.g. Chinese language &
literature).
