Kurt Landes, the Suns' general manager, said the announcement was delayed because the Bombers were in the league finals last week. They were the South Atlantic League runners-up.
Minor league and major league teams have about three weeks this month to look into changing affiliations.
Landes said the Mets were the Suns' first choice.
Rich Neumann, the vice president of development for Mandalay Sports Entertainment, agreed. "We consider the Mets to be a first-class organization," he said.
Bobby Evans, the Giants' director of minor league administration, said that communication was good with Landes, but not with Mandalay - leaving the Giants wondering if the owners were devoted to Hagerstown and a new stadium.
However, Neumann said Mandalay kept in touch and made its commitment to Hagerstown clear.
Evans said the Giants also were leery because Mandalay purchased a Giants' affiliate in Shreveport, La., a few years ago, moved it to Frisco, Texas, and aligned it with the Texas Rangers.
Neumann declined to comment on that situation.
With the Mets, Landes said, the Suns should have "a more consistent quality of product on the field. ... We owe it to our hardcore fans that go to the games and want to see wins."
This season, the Suns were 49-88, last among the Class A South Atlantic League's 16 teams.
Starting in 1998, the Suns reached the playoffs three out of four seasons, but missed the next three years.
Landes said Baseball America, a trade publication, listed the Mets' minor league system high this year and the Giants' system low.
The Mets were ranked 10th-best out of 30 teams, while the Giants were ranked 24th.
The rankings can vary widely year to year. Two years ago, the Giants were ranked 12th and the Mets were ranked 27th.
Another Mets' farm team, the Brooklyn Cyclones, reached its league's playoffs this year. With the affiliation switch, several Bombers and Cyclones could end up in Hagerstown.
The Bombers were connected to the Mets for 22 years, said Rich Mozingo, the Bombers' president. "We just decided it was time to go in a new direction," he said.
Kevin Morgan, the Mets' director of minor league operations, couldn't be reached for comment Monday afternoon, but in a statement released by the Suns, he said, "We're happy to be in Hagerstown. Their operations are run in a first-class manner and it's going to be great for our players to play in the atmosphere there. We're looking forward to a long partnership."
Landes said there are benefits to linking to an East Coast organization.
Hagerstown baseball fans who travel could follow their favorite Suns as they move to Mets' affiliates in Virginia, New York, Florida, South Carolina and Tennessee, Landes said.
Also, with the time difference, it's easier to watch the Mets' televised night games and to find results in the next morning's newspaper, he said.
Landes said the Suns had backup choices in mind, but the Montreal Expos - which might soon move to Washington, D.C., or northern Virginia - were not one of them.
The Suns were affiliated with the Baltimore Orioles from 1981 to 1992 and the Toronto Blue Jays from 1993 to 2000.