In Julius Caesar, who is the most noble, Brutus or Caesar?

Brutus is the most noble.  He never acted out of
self-interest.  He always thought about the good of Rome.  He didn't kill Caesar out of
hate, but out of love for his country.  He also wanted to limit the bloodshed as much as
possible which is why he told the conspirators to spare Antony.  Brutus isn't perfect,
but morally he's quite sound.

Caesar is in the middle,
because although he is ambitious, he also cares deeply for his friends and his country. 
He showed excess ambition when he killed off Pompey (before the play began).  He also
showed how badly he wanted that crown and how angry he was when the people cheered the
fact he declined it.  Still, people like Antony were loyal to him because they knew he
was a great man.  His will also showed his love for Rome and its people.  When he
realized Brutus was among his assassins, he was genuinely hurt because he took Brutus in
as if he were a son (this too wasn't part of the
play).

Cassius is the least noble.  He operates purely on
self-interest.  He wants power and knows he'll never get it if Caesar is around because
Caesar doesn't like him.  He knows Brutus' weaknesses and exploits them to trick Brutus
into thinking Caesar needs to die for the good of Rome.  He proves to be a plunderer in
Act IV and  acted in the same corrupt ways he criticized Caesar for in Act I.  Never
once did Cassius do anything for anybody but himself.