it will depend on what you would define as "good bah kut teh", where u prefer one that has a stronger herb taste to the soup or whether you prefer one that has a stronger meat aroma in the soup.
if u're a lover of the former, the one that i've best tried so far is the one that is opposite The Concourse/Shopping Mall at beach road. i doubt u can miss it as it is facing the main road, and it has pictures of the U-magazine food directory with Sylvester Sim on the cover all around the shop. sorry that i dont have the name of the shop ^^". you have a choice of whether to eat it with rice or mee sua.
if u have a soft spot for the latter, then u'll have to travel all the way to the Food Centre, that is next to the East Coast Lagoon's Cable Ski Park, that is in East Coast Park Area E. okay, i know this sounds a tad confusing, but if u happen to be jogging, or cycling or blading in ECP it'll be a lot easier cos it's down the track.
here's the webbie of the map: http://www.nparks.gov.sg/imgs/maps/ecp-ef.gif
it goes by the name of "Han Jia's Bak Kut Teh" i think. Han being the english translation of the chinese surname 韩家. hmm not too sure if u can view the chinese.