Both men were given a nine out of 10 for their performance but Mr Power won because of his high workload and skill.
A third of government legislation in 2010 was from Mr Power, and he was in charge of reform of the justice system, financial markets and liquor laws.
"He's like a lock to Key's role on the wing," political newsletter Trans Tasman said.
Mr Key had another great performance as prime minister but needed an agenda going forward, it said.
"He is the master of the 6pm TV soundbite and has excelled himself in the crises which have engulfed the country this year."
Last year's politician of the year, Speaker Lockwood Smith, fell from 9.25 to 8 because he of his handling of travel allowances.
Deputy Prime Minister Bill English scored 8.5 out of 10 and Trans Tasman said more was expected of him.
Labour leader Phil Goff scored six, having shown more confidence, but he was still robotic and failed to connect, Trans Tasman said.
Deputy leader Annette King, whip Darren Hughes and David Parker were Labour's top scorers on 6.5.
Former Labour minister and now independent MP Chris Carter joined National MP Paul Quinn at the bottom of the rank, both scoring just one out of 10.
Mr Carter's "egregious sense of entitlement brought his downfall", Trans Tasman said, while Mr Quinn was rude, arrogant and a "media-loathing misfit".
Labour MP Ashraf Choudhray was also among the bottom ranked with 1.5.
Former Cabinet minister Pansy Wong was given two out of 10 following her travel perks scandal.
Law and order select committee chairwoman Sandra Goudie was given 2.5 and Trans Tasman said it was time for her to be removed as chair.
"The committee at times has been a dysfunctional mess. Abrasive Labour MPs haven't helped but she isn't hacking it."
As well, she was difficult to deal with.
