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).