I didn't read all the above replies in detail, but in case this wasn't covered...
In the public system, if all seems to be going to plan you will mainly see midwives (or your GP if you do shared care)
But if ever there is anything wrong or risky they will arrange for you to see one of the hospital obgyns. It might not always be the same one, but don't feel like you won't get to see the specialists if you need to.

I use a private ob, but that's mainly so I can choose the hospital and dr that delivers my baby. I would actually much rather a midwife or GP model of pre-natal care! No point seeing the ob for all the routine visits in my opinion!