Hi fellow Sydney rider.
I ride from Annandale to North Sydney. The recommendation to find a good local bike shop is spot on if your new to it. I ride a Kona MTB with slicks. This works well for me (20km round trip). But I'm considering the hybrid option. The advice to look at disc brakes sounds good too. In your case stopping (in wet and dry) is probably more important than going fast. I've tried some Hayes hydraulic disc brakes, they feel really good. Stick to the wider tyres - Sydney streets are pretty crappy and you'll spend your time dodging potholes if you go down the road bike with flat bar direction.
Good luck.
ER