I'd stick my neck out to say that Hong Yuan Prawn Noodles (Bestway Building, near Tanjong Pagar MRT) offers probably the best prawn mee in the CBD, and it is indeed a mighty fine effort, capable of matching the top guns such as Beach Road, Jalan Sultan, Hoe Nam and the rest. it may perhaps lose out to Wah Kee but it's really a very high bar already.
Hong Yuan sells traditional Hokkien prawn noodles, i.e. cooked with pork ribs and prawns. I ordered the dry version - how did it taste? I took my first sip of the thick, richly-coloured soup (which augurs well): wow, I was impressed. The soup was a rich thick "gao" broth that was bursting with depth of flavour and had an intense taste that was still quite well rounded, with a subtle sweetness. Yes, I enjoyed it a lot that I had a second bowl.
The gravy that adorned the noodles were superb as well - there was a lovely umami flavour from the chilli. The noodles were also well-cooked: smooth kway teow. Altogether: 8.25/10