so did you go with Dr Vanaja in the end? What I can tell you is that she was the nurses choice since years ago, even when she was just Consultant. Many of the S Cons in NUH are great and have been around for a long time. Arjit Biswas, as mentioned before, is great as well. Or Anupriya Agarwal---I have a friend who had an op under her and was very happy regarding her operative skill. If you want a Chinese female, then Su Lin Lin is popular--so popular you might not get appointments. In general you won't go wrong with any of the S Cons in NUH(the ones below age 70 pls...). Same for KKH.
Private wise, there are many to choose from. If you're into fertility, you can just go for one of the big names. If its expensive, consider overseas fertility treatment or subsidised in the public hosp.
For ultrasound birth check and detailed explanation, amongst the most skilful obs I have seen would be Chia Yee Tien in MtE. Though with the Harmony and Panorama these days, its kind of made a fair bit of the ultrasound less useful as a diagnostic tool.
An example would be the sex of the kid. At 10-12 weeks, the ultrasound can't tell boy or girl for sure. But a blood test for Harmony/Panorama will tell with almost absolute certainty. But ultrasounds can check for structure defects like limbs, fingers, heart, head, and twins etc which the blood tests cannot.
also, need to decide if you want epidural during kid-popping.
In the end, the obstetrician is there to assist. you will pop the kid in most cases with no help whatsoever. For thousands of years, women have popped kids with no problems!