forget the stats, especially regular season stats. For me, it's all about the playoffs and big games. Certain players just have that special something that enables them to play their best when it is needed the most.
Everyone points to the Miami series when Rondo almost single handily willed the Celts to a win. But, for me, it goes back to the championship season of 2008. Pivotal Game 5, Cavs are just kicking the Celts' butts late in the first half. Under 3 to play, down 12 and 1 second left on the shot clock, young Rondo (2nd year, first playoff) hits a 3 (from the corner, IIRC). After a stop, Rondo comes down and pops another 3 (early in the possession, ultimate confidence) to cut the lead to 6. Celts finish the half only down 3 and win by 7.
That is a player with championship pedigree, a player you go to war with.