This "who is the better vocalist" is a popular topic around the Beatles forums right now.
Sadly, it develops too often into Paul vs John battles. And I blame the Paul fans here. Many (not all) Paul supporters cannot take any criticism of their hero. And this angle is no exception. They say, Paul had a stronger voice, greater range, more sensitive, yadda yadda.
I say to them, go listen to a whole Beatles album: any will do. (cept AHDN, where Lennon dominates too much). Then, look as honestly as you can, deep into your heart ... and don't you agree:
A) Paul is a very good singer ...
but...
B) John sent shivers up your spine.
If GREAT rock singing means anything, then John Lennon HAS to be THE man.