The biggest song basically base on performance locally and internationally of the song on charts, sales, streams, downloads and of course the overall impact.
For 1st and 2nd Generation is mostly local chart performance since most global data around that period is almost unverified so it’s better to be base on Korean charts.
1st Generation: I’m truly blank for this one it could be a song from SES, Seo Taji & Boys, HOT, Shinhwa or god.
2nd Generation: I think the top 5 contenders are:
1. Gee
2. I am the best
3. Roly Poly
4. BANG BANG BANG
5. Nobody
For 3rd and 4th Generation internationally performance can be counted more just as the korean stats.
3rd Generation: We have many hits in this generation top 3 is:
1. Spring Day
2. Dynamite
3. Cheer Up
4th generation: People might argue either Aespa Next level or Itzy Wannabe.