Hey, thats a very detailed explanation and research you have done all the 3 unis. Unlike you, i did not have the options to choose which uni that offers better econs degree but i do have some research and readings on the different unis.
Firstly, i didnt apply to Smu as i do not feel i am comfortable in the environment of achieving high class participation, not sure if it applies for Smu econs but generally. And i read somewhere that, compared to Nus/Ntu, smu economics is not as rigorous in terms of theory. However, i feel the internship and the high class participation style of teaching certainly boost the chances of getting a job after graduation.
Secondly, for NUS. I guess most people who went FASS do take econs as a major and the large amount of cohort may seems to be of a greater competition. I am not so sure about how the bell curve will affect the results but i guess like you said, competition is everywhere.
In terms of reputation , Nus definitely had an edge over Smu or Ntu. Especially if you plan to go overseas to work or exchange programmes.. However the only bad points about NUS econs is perhaps during the first year, where everybody has to take 3 exposing core modules which i personally feel is a waste of time if you know what you want to do. Hence, i think its a double-edged sword(good for those who are unsure!).
Lastly, for Ntu econs. Perhaps not as reputable as Nus or popular like Smu. But i think theres still some attractive points about the school. Like you said, the small cohort may make the interaction with the professors better. Direct honours can be viewed as a double edged sword too. On one hand, it definitely does not guarantee you to get Honours after 4 years, but it definitely motivates you to do well if not you wil be wasting 1 more year. As for internships, since it is compulsory to do in Ntu i guess its rather good. Although all other unis encourage their students to take internship during semester breaks.
As for working in public sectors, i personally feel there isnt any much difference between NUS or NTU, perhaps the school culture...
So thats just my 2 cents worth of sharing but i do hope seniors out there could prove me wrong or backup my words as i am just viewing this from the perception of an outsider.