It is Carmelo, Carmelo or Carmelo. It is not a close . A distant second would be Warrick, one of the most underrated SU players ever. Very, very talented. I would also think that Wes Johnson and Arinze Onuaku merit some consideration as they were instrumental in restoring SU back to the top of the NCAA world after some mediocre years after the championship year. As for GMAC, a very good player, but I am not sure I understand the love affair SU fans have with him. He is a great best man, not sure he was such a great groom (except in the Big East Tournament).
Here is the ultimate answer. If GMAC but no Carmelo, SU does not win a national championship under any circumstances. If Carmelo, but no GMAC, we very likely still win the title. Carmelo over anyone else by a landslide.