I find this whole discussion extremely obsurd. Trezeguet is an excellent striker and fits into the Juventus system very well. Gilardino is a good striker who is trying to reach his potential. And Luca Toni is one of the top 3 strikers in the world. I can only think of Thierry Henry and I even have my doubts on him, when I think of a possibly better striker.
Toni is clearly a better striker. No one can match what he brings to the pitch. He fit excellently in Lippi's Italy team. Came back to the Italy squad when Donadoni took over and immediately made a huge impact. He does more than just score the most goals in the toughest league to score goals EVERY YEAR. He controls the opposing defense and sets up huge free kick opportunities by frustrating defenders into hacking at him.
He scores, creates plays, and moves extremely well off the ball. He has a lot more ability than people give him credit for. He plays and moves all over the box and drops back to a good depth as well. If this is a who is better discussion, unless you are completely biased, this should be a quick debate. If this is a: do we bring him along side Trez next year or Swap one for the other, then this debate has validity.
But, there is no question who is the best striker out of the bunch. The guy is amazing and is truly a one of a kind type of player. He is everything you could want in a striker, especially when considering that if he played at Juventus, he would play with Del Piero who could be the perfect couter-part for Toni.
It all comes down to Juventus' funds.