In stand-to-stand combat, I'd say both of them are about equal, with Star Platinum only having a very slight edge in terms of physical ability, not enough to inherently win the fight though. Through scaling, Bruno has his durability because he survived King Crimson, whom got his attack potency because he managed to eviscerate Polnareff. Using this line of scaling, Star Platinum should probably be superior because Star Platinum has easily overpowered both Magician Red's flames (when he casually broke out of his Red Bind) and actual strength (when he casually choked him with a single fully extended arm, while MR couldn't do shit about it). This is important, because we know Silver Chariot is much weaker than Magician Red physically, seeing as how he lost to his flames in a fight, and was physically incapable of doing anything against Judgement, and needed Magician Red to come kick the shit out of Judgement, rescuing Polnareff. This means through scaling, surviving someone who eviscerated Polnareff is much less impressive than single-handedly overpowering the man, who had completely outperformed Silver Charot and Polnareff on two seperate occasions. Just to clarify:
Jotaro/SP > Avdol/MR > Polnareff/SC
Avdol/MR > Judgement > Polnareff/SC
Diavolo/KC > Bruno/SF >/= Polnareff/SC
And therefore, through scaling, Jotaro/SP > Bruno/SF, even if it's not by much.
(Admittedly, this may just be me thinking in terms of plot, and not a true vsbattle.)
Star Platinum is a relatively haxless stand before the encounter with DIO, so Jotaro is at a big disadvantage. The question is can Jotaro with his relatively small strength advantage and combat experience, able to beat Bruno? I'd say yes. Arguably, Jotaro has been up against far more opponents, and should have more experience than Bruno (stopping short at DIO). I see this fight falling in line with the rest of the fights he's been in; fight begins, opponent explains stand ability and shows how much of a gap in their ability there is, Jotaro says "yare yare daze" and reveals that he isn't a noob and his opponent is severely underestimating how much strength, speed, and intelligence he has, and proceeds to take advantage of the situation.
Besides, the ability to open zippers isn't even that great in terms of combat. It's more utility if anything, with the added ability to disable people if they get too zipped(?), but that's not a problem when you have a stand as strong and fast as Star Platinum.
If their stands ever get intertwined in a physical duel leaving the users open, Jotaro would clearly whoop Bruno's athletic human tier ass. I doubt a gun would even phase him, having gasoline shot into him and leaving a hole the size of a rock didn't. He'd just beat Bruno's ass, weakening his strength with Sticky Fingers and letting Star Platinum overpower it.
It's a pretty close fight upon first glance, but with a closer look, Jotaro has more combat experience as a result of being a main character, and should be stronger as well. Therefore I vote Jotaro.
