Base it on:
- Vocals/Rap (great at one plus at least average at the other)
- Dance
Extra things: (obviously not super important, but still large parts of K-pop)
- Visuals
- Variety skills/personality
- Stage presence
- Composing
- Producing
- Writing
For me, the ultimate all-rounder (of the 4th gen at least) is still Choi Yena, this girl can sing, dance and rap well above average, is great at variety and imo has great visuals & decent stage presence
Other strong contenders: Monday, Seulgi, Karina and Winter (I hate SM but they really do have some insanely talented idols)
Edit: Let me add Soyeon and Jennie, who I forgot about. Also I don’t know much about boy group members which is why I haven’t included them, but feel free to add them as well