- He is the best boy in the class.
- He is the better boy between them.
- He is the better boy in the class.
What about the above sentence?
of the three I find the first sentence to be correct
if there is a comparison to be made then better is usually limited to two as in “you are better than me” or “of the two I consider the first to be a better choice”
same goes with sentence three - class refers to a large number
He is the better boy between Rahim and Karim.
What about the sentence?
That would have to be
'He is the better boy of the two: Rahim and Karim.