I think there should be a comma after either option. "It's better for we/us students" does not seems right to me.
However, I'm learning english so I might be totally wrong about it :)
What did I say? I meant to say there should be a comma after 'us'... the option I voted for... 'We' is wrong (just for the record... and my teacher! :) )
With a comma, a teacher is talking to the students. Without the comma, a student is talking to the teacher or fellow students.