i've had excellent care (for the most part) in the public system... i'm going to be delivering next week after being hospitalised 4 times throughout my pregnancy.
the doctors are VERY thorough! but keep in mind that Queen Mary is a teaching hospital, and so you may from time to time be confronted with a clueless med student...keep your cool and ask to speak to the doctor in charge of your case.
there's one doctor that i've come to know though all of my visits, and i really really like her, i'm a little disappointed that she's not the one who'll deliver my boy, but the doctor that will probably do it is quite good too.
as for ultrasounds, i've been lucky. because of the complications with my pregnancy, the dr that i really like asked me very early on if i would be interested in taking part in a study...what did i have to do? go once per month for a 3D ultrasound scan so that she could watch the development of the vascular system of the placenta! so, i got 6 free 3D scans (she gave me photos each time!) each scan was worth about $1200!!!
before i knew that i'd be doing this study, i had the 12 week scan at tsan yuk and had to pay $290 to get one photo...ah well, my boy is the most photographed child ever (and he isn't even born yet!!!)
good luck!