Cunliffe is able to crisply articulate Labour values with verve and passion. He is supremely bright. But he is not liked in the caucus. He oozes self-confidence, and sometimes this translates into an arrogance that gets the better of him.
It is a character flaw which could derail him in a job where it would be noticed and would typecast him.
Parker comes across as bookish, the archetypal policy wonk. He can be passionate when angry. But he is seriously charisma-challenged. He has to persuade his colleagues he brings more to the role of leader than simply being the anti-Cunliffe candidate.
Shearer, who possesses some of John Key's knack for the common touch, will try to come through the middle by selling himself as someone who has all the positive qualities of his rivals and none of their negatives.
His major handicap is that he is largely unknown to the public. Unlike Cunliffe and Parker, who both served as ministers in the last Labour government, Shearer is untested. Apart from developing Labour's research and development policy he has made little impact since coming into the House following a byelection in Helen Clark's old seat.
Shearer, however, has nothing to lose by entering the race. Even if he pulls out of the contest through lack of support, that will not affect his future leadership prospects.
And another leadership contest may come sooner than later. Whoever replaces Phil Goff is already being lumbered with predictions of failure to match or better John Key, inevitably prompting a leadership spill before or after the next election.
By that stage other contenders - such as former party president Andrew Little - may have emerged to vie for the job, alongside the likes of Wellington Central's Grant Robertson and list MP Shane Jones.
A reasonable showing would guarantee Shearer's already-likely promotion to Labour's front-bench and position him near the head of the pack.
