I live on the east coast and there is a place on the corner of Still Rd and Joo Chiat Place that gets very high marks from most of the locals I talk to. It's only a 10-15 minute ride from the Marina hotels. By the way, it nearly always has a long queue (I'm not sure that means too much in Singapore, because people actually seem to enjoy waiting in line here!). I'm not actually a big fan of this type of crab, so I cannot personally attest to whether this place is the "best."