So, what's wrong with "today's best artists"? Sounds more natural to me.
He is among the best of today's artists. Rejected.
He is among the best of today's artists. Rejected. Reported.
He is among the best artists of the day. Rejected. Reported. Jan 2020.
This is still marked as incorrect. I think a native English speaker would use "the day", but I suppose it's not a literal translation. I have also reported it.
what is wrong with "He is among the best artists of today? Perfectly good English.