John DeStefano Jr.’s decision not to seek re-election after 10 terms as the city’s mayor leaves a vacuum in New Haven politics far larger than the space normally reserved for his name on the ballot.

Several candidates, transformed overnight from unlikely challengers to serious contenders, have already emerged to replace DeStefano when the next mayor will be sworn in on Jan. 1, 2014. Although only three — Ward 10 Alderman Justin Elicker FES ’10 SOM ’10, State Rep. Gary Holder-Winfield and plumber Sundiata Keitazulu — have officially declared their candidacies, two others have strongly suggested the possibility of running. At least three more are considered possible candidates, making this year’s race the most competitive in more than two decades.

Despite the plethora of potential candidates, individual policy priorities are unlikely to differ significantly, with contenders all emphasizing fiscal responsibility, education reform and crime reduction throughout the city. Rather, voters will choose between vastly different personalities and management styles.

“The next mayor has to listen to his constituents more, has to listen more to his Board of Aldermen, and has to be more transparent,” Ward 29 Alderman Brian Wingate said.

City officials interviewed said they hope the next mayor will capitalize on DeStefano’s successes, such as a revitalized downtown and improved town-gown relations, while avoiding issues that have become persistent stumbling blocks for the mayor. Several noted DeStefano’s often-tense relationship with the Board of Aldermen and a governance style Democratic Party activist and Board of Alderman candidate Charlie Pillsbury considered “one-party rule.” “I believe the person [who becomes mayor] has to be somebody that not only has a vision and passion for community, but also understands checks and balances,” Ward 16 Alderman Migdalia Castro said.

Both Elicker, who announced his candidacy at an event last week, and Holder-Winfield, who told the News Tuesday night he planned to file paperwork to run for mayor on Friday, have emphasized transparency and connecting with constituents as major planks of their platforms.

Likely candidates beyond Elicker and Holder-Winfield include Hillhouse High School Principal Kermit Carolina and Probate Court Judge Jack Keyes, who served as city clerk nearly three decades ago. Carolina, who refused to support DeStefano in his 2011 re-election bid, has publicly come up against the mayor on a variety of issues, including his three-day suspension over an alleged transcript-tampering scandal in 2012.

“I am strongly considering running for mayor,” Carolina said in a statement Tuesday, calling DeStefano’s retirement “exciting because it opens up opportunities for new leadership and energy in the city.”

State Senate Majority Leader Martin Looney, a longtime law partner of Keyes, Board of Alderman President Jorge Perez and State Rep. Patricia Dillon are also possible candidates. Although neither Looney nor Dillon has publicly considered running, Perez admitted Tuesday, albeit subtly, that he may run, responding “I’m not ready to say,” when asked if he was running for mayor.

“Over the next week or so, I will be talking to my family, my colleagues, my constituents and others, and only then will I make a decision concerning in what role I will continue to serve the city,” he said in a statement.

Looney remained noncommittal, telling the New Haven Independent Tuesday, “I don’t even want to discuss [a mayoral candidacy] at this point. It’s far too early.”

Democratic Town Chairwoman Jackie James, who told the New Haven Independent Tuesday that she would not run for mayor, said that she has not put her support behind any candidate yet.

Exactly where the candidates stand against each other is uncertain. A recent poll commissioned by a group of Connecticut labor unions put Looney and fellow State Sen. Toni Harp in the lead, although Tarp told the New Haven Independent Tuesday that she would not run.

Challengers will face off in a September Democratic primary before moving on to the general election in November. Winning the primary has traditionally meant winning the general election, which no Republican has claimed since 1951.

Candidates who elect to run will have to decide whether to fundraise themselves or make use of public financing — an initiative once triumphed by DeStefano that would provide $50,000 in campaign funds.