Of course best is open to a bit of interpretation but overall I'd vote for Calzaghe, he best Kessler pretty well and Kessler went on to have a pretty good career, he beat froch fairly comfortably first time out I(and the judges) thought and he went on to be pretty good... Calzaghe also overcame an fairly old but still going strong Hopkins, I wanted Hopkins to win and I just don't see how you could give him that win... Calzaghe went undefeated for such a long and even though he lacks a lot of prime big names I think he did pretty great.. (I forgot about the lacy demolition :S)
Of course Hamed was something else at the time but Barrera really did him in, great talent though but I'd stick with Joe...
Also Hatton deserves a mention too he only lost to two legends, as annoying as floyd is he's just a great boxer and Pacman was on a rampage at that time. And Hatton despite being quite a drunk away from the ring got himself in shape and won a good few fights... Now there's talent!
And obviously I haven't seen a lot of the other guys mentioned, I was pretty young when benn and Eubank were around, Hamed was the first one I can remember well.
And of course lennox isn't mentioned as he's the number 1 Canadian of the last 40 years