Stronger in what way?
Physically, Star Platinum is stronger.
But overall, I'd say The World is superior due to having a longer time stop. You literally have more time to do things. Also, Star Platinum's resistance to time stop isn't long enough compared to 9+ seconds.
If you get rid of time stop and just do physical abilities it goes something like this:
The World is slightly faster than Star Platinum
The World has more range than Star Platinum (for some reason)
Star Platinum is physically stronger than The World by a good margin but they can still box with one another
Star Platinum most likely has more durability than The World considering it was tanking a lot. The World was literally cracking and breaking during the fight. The only time this happened to Star Platinum was near the end, and it was minor.
Really. The fight could've gone either way. Star Platinum's physical abilities outmatch The World's but The World's "ability" abilities outmatch Star Platinum's.
Ironically, if DIO hadn't done his road roller move and approached Jotaro from a different angle, he could've beaten him. But he didn't.
Alternatively, Star Platinum itself is capable of defeating The World because... Well... It did.
Either of them could've killed the other under different/multiple circumstances.