Agreed, Viet food is lacking in SG. For various reasons it hasn't caught on with the locals. Still, the average quality level of those Viet places that do exist is higher than that in the US.

As for hawker food, the increasing cost of doing business in SG means that hawkers use cheaper ingredients and give you less meat/fish. For dishes of Malaysian origin, Penang is the place to go for the best of the best. Even many Singaporeans will admit this.

I'd go with Bangkok as my personal #1 food city in Asia, but Viet cuisine is lacking there is well. So maybe Saigon?