Harry?
Harry looked like the simplest option. After all, Harry had obtained the Philosopher's Stone in the original work, but if the Philosopher's Stone as a whole was just a trial, the moment Harry obtained it, he would have already completed the trial. If Murphy wanted to get the Philosopher's Stone from Harry after that, he might need to face Dumbledore directly.
Moreover, Harry was also a figure monitored by Dumbledore throughout the entire process. Once Dumbledore realized that Murphy was interfering, he might intervene directly as well.
Unless Dumbledore's entire setup really was just to protect the Philosopher's Stone and didn't involve more monitoring and intervention regarding Harry and the process itself, then that would still be a possibility.
But if that were the case, it wouldn't be much of a problem for Murphy to go and get it directly, completely eliminating the need for a proxy.
He had better consider it from the worst-case scenario.
Harry could only be temporarily abandoned.
Quirrell was directly controlled by Voldemort, so he couldn't be touched either.
Snape and the other professors were all difficult to deal with, so he still had to choose from among the students...
Neville Longbottom?
Too foolish.
Ron Weasley?
Too weak.
Hermione Granger?
Perhaps that could be considered...
As he thought about it, a thought suddenly jumped into his mind.
There was a fellow who might be of some use.
"Diary, no, Tom. Long time no see."
In the Chamber of Secrets, Murphy took out the diary that had been gathering dust for a long time.
To this day, through the study of various mental magics, Murphy had roughly figured out the principle behind the diary.
Aside from being a Horcrux that housed a piece of Tom Riddle's soul, it could also seize the target's magic