Vettori is the best one-day international spinner, an irrefutable claim extending back to last century. He also infuses the team with intangible confidence as a senior player. However, if McCullum saves more runs in the field and hits at a better strike rate in the closing overs, does that give him a selection edge?
Let's don a dispassionate anorak and thumb through some statistics.
The pair's core role would be as spinners offering variations to a three pace bowler attack on most pitches, with assistance from the likes of Corey Anderson, Grant Elliott or Kane Williamson.
With just five wickets in eight ODIs this season, Vettori's average is 61.20, but the key number relating to his role is 4.37, an impressive economy rate which enables him to contain batting line-ups with guile and accuracy during the middle stages of an innings.
McCullum struggles to match Vettori on this count with an economy rate of 4.96 and average of 48.83, also from eight matches in 2014-15. Extrapolating that out across 10 overs means Vettori might take one for 44 and McCullum one for 50.
This season hasn't provided a huge sample of their batting capabilities. Vettori's averaged 13.75 in six innings with a strike rate of 108; McCullum's averaged 24 in five innings at a strike rate of 63. They've both had difficulties. Vettori had to bat at No5 in Hamilton in Kane Williamson's absence.
McCullum's relatively sluggish 25 off 47 balls guided New Zealand to their three-wicket victory in Christchurch and he was forced to bat conservatively for 13 off 26 balls in Hamilton, when the team innings threatened to freefall at 183 for six in the 37th over.
His 119 off 109 balls at No5 for Otago against Wellington in Queenstown on December 30 showed he's still capable of finding the sweet spot.
Their career ODI strike rates indicate McCullum has a slight edge with 87 runs per 100 balls compared with Vettori's 82, but the former captain's batting ability improved markedly late in his career.
So on to fielding. Both have safe hands but, while Vettori never lets the side down, McCullum's athleticism is exceptional. His average catches per match (0.47) top Vettori's (0.29).
Yet while statistics are important to measure a player's ability, unquantifiable figures also play a part.
McCullum's reputation continues to build but just seeing "DL Vettori" on a team sheet adds a different psychological dimension for both teams. There's also the instant advice Vettori, as a former captain, might offer Brendon McCullum without requiring a pow-wow at a drinks break.
Perhaps the most significant factor in the debate is that the pair seem mature enough to prevent the rivalry obstructing the overall team effort.
The fourth match in Nelson provided an example. As the New Zealand chase started, a padded-up Vettori and a McCullum tossing a ball in his hand appeared headed to the nets for some throwdowns. Vettori subsequently hit the winning runs in the penultimate over.
That highlights the sort of internal competition and support the New Zealand team will need to achieve their best at the World Cup.
