One week into the reign of Mayor Bill de Blasio, the City Council will meet to choose a new speaker -- New York's second most powerful official.

Councilwoman Melissa Mark-Viverito of East Harlem is the strong favorite to win today. But our choice would be for Councilman Daniel Garodnick of Manhattan's East Side to prevail in the backroom swap-meet that passes for the council's selection process.

Mark-Viverito of East Harlem is too closely tied to Mayor Bill de Blasio, who -- behind the scenes -- guided her trajectory toward the job. A big part of the speaker's job is to serve as a check on the mayor's sweeping powers.

How can that happen when the mayor is the principal sponsor of Mark-Viverito?

De Blasio's role alone should be a deal-breaker.

But there's another problem. Media accounts have revealed that Mark-Viverito failed to report years of rental income on city ethics forms, a lapse she called an honest mistake. Maybe so, but it still raises questions.

For his part, Garodnick was a driving force behind the city's Green Energy Code to cut greenhouse-gas emissions in buildings throughout the city. And he played a key role in passing the Tenant Protection Act that shields renters from harassment by landlords.

Garodnick's primary supporters for the speakership are the Democratic leaders of the Bronx and Queens, unlikely avatars for fearless political reform and exacting standards of administrative accountability. But Garodnick would come to the job with far less baggage than Mark-Viverito.

The mayor commands all municipal agencies and an army of more than 300,000 workers. The mayor basks daily in the bully pulpit of the media and gets first crack at drafting an annual city budget of around $70 billion.

The city needs an assertive speaker in the face of that power -- when it comes to land-use proposals, deciding what stays in the budget and what goes, and determining when it's time to override a mayoral veto.

The system of checks and balances works -- and the council should embrace it.