Hi
two most popular doctors are TC Chang or Paul Tsang. They are both at Thompson Medical which is by far the nicest ward for the deliveries.
Now depending on the type of the birth that you would like...if you are very pro natural and would like to go through labour as natural as possible, then Paul Tsang is your guy. TC Chang is also very pro natural birth but is little bit more open to suggestions etc.
If you are very pro ceserian, then Dr Ann Tan at Mt E is your way fwd as she likes to "manage" her patients and is not very pro-natural birth without any intervention.
Personally i would go with TC Chang as many of new mums always speak very highly of him (and Paul Tsang too)
http://www.doctor-chang.net/home.asp (link for tc chang)
http://www.healthcare.com/profile/paul-tseng/ (paul tsang)
http://www.anntan.com.sg/eng/Profile.html (ann tan)
Hope this is helpful.