Do you think Harry Potter would have ended up in Slytherin if he had sat with some kids on the train
Would Harry Potter have chosen the House of Slytherin under other circumstances?
Sure; the Sorting Hat thought he was more compatible with Slytherins anyway and the Sorting Hat was never wrong.
"Difficult. Very difficult… …a nice thirst to prove yourself, now that's interesting.... So where shall I put you?" (Sorting Hat) Harry… …thought, Not Slytherin, not Slytherin. "Not Slytherin, eh?" said the small voice. "Are you sure? You could be great, you know, it's all here in your head, and Slytherin will help you on the way to greatness, no doubt about that…” Harry Potter and the Philosopher’s Stone – J.K. Rowling
Draco Malfoy didn’t do his house any favors the first day he met Harry in Madam Malkins. If Draco had shown just a little less haughtiness, he might have gotten off to a better start with Harry; as it was, that was strike two against Slytherin.
Still, that could have been overcome if Harry hadn’t sat next to Ron Weasely if Harry had instead been seated with other Slytherins. After all, we are (lamely) told post-publication that Slytherins weren’t all bad.
But the greatest hurdle House of Slytherin faced started with Rubeus Hagrid’s immediate prejudice against anyone in the House of Slytherin; you can’t blame Rubeus, considering Tom Riddle got him expelled from Hogwarts, but Harry was unduly influenced from the start, all the same.
Hagrid made it clear that it was a Slytherin who killed Harry’s parents, so Harry was never going to take the cotton to that house. But if Hagrid had kept his mouth shut, the fact that Voldemort was a Slytherin might have been less of an issue.
So, the spirit of the question really comes back to whether Hagrid might have shed a bit brighter of light on Slytherins, more so than if Harry had just sat with someone other than Ron Weasley.