How to best correctly spell this sound?

Solution 1:

I'd go with ooooh, and let the reader work out the pitch change from context:

"I'm so sick and tired of you always asking me questions, Benjamin! Pack your things and report to the principal. I won't have you in my class." Mr. Smith yelled. Benjamin's class mates mocked him "ooooh" while he quickly packed his things and left.

or

"I'm so sick and tired of you always asking me questions, Benjamin! Pack your things and report to the principal. I won't have you in my class." Mr. Smith yelled. Benjamin felt on top of the world and his class mates cheered him on "ooooh" while he packed his things and left for principal Puddlefrock's office.