I've been living in Vietnam for the last two years and my life here as a foreigner is pretty sweet, all things considered.
But I'm not sure I'd feel the same way if I were a native. The fact that I can buy a plane ticket tomorrow and be half way around the world any time makes it easier to ignore some of the realities that natives face without that freedom.
The Singapore passport is pretty good. It's supposedly better than Iceland in terms of travel freedom. [1]
However, I personally think the government has implemented considerable measures to stop brain drain, including 4/6-year bond government university scholarships [2] and an intended lack of (usually bilateral) working holiday visas [3].
(Can't find any links aggregating such visas for Singapore citizens, but I found that New Zealand might be one of the few countries to offer such a visa [3]. There's no such programme for Australia [4], Canada [5] or the UK [6] — this could be contrasted with Malaysia, which has bilateral programmes with some of these countries.)
On the bright side, the USA offers the H1B1 non-immigrant-intent visa for Singapore citizens. [7]
Vietnamese are free to travel outside Vietnam and even emigrate but the reality is that visas for most countries outside SE Asia are hard for them to come by and they certainly don't have the luxury of jetting back to the U.S. any time things get uncomfortable for them.
But I'm not sure I'd feel the same way if I were a native. The fact that I can buy a plane ticket tomorrow and be half way around the world any time makes it easier to ignore some of the realities that natives face without that freedom.