.......if Giorno met DIO? I think DIO would try his best t be a good dad, if not out of love, then spite for Dario.

If the Eyes of Heaven battle quotes are to be believed, they would use eachother for their own gains until they betray eachother. Unfortunately for Dio, he doesn't have G.E.R.

I've seen other people discuses this. DIO's moral's conflict with Giorno. While Part 6 will demonstrate that DIO can be a civil person if he doesn't hate you, DIO's megalomania and lack of empathy would definitely rub Giorno the wrong way.

On the other hand, DIO would admire how Giorno seized power and made a role for himself by his own force. But he'd probably think Giorno is too soft otherwise. Also, Giorno's proactive, forge your own path attitude wouldn't sit well with DIO, because that means he couldn't count on his loyalty and would always have a feeling that he would betray him.

Part 6 Spoiler:I've also seen people say that Donatello would be DIO's favorite.