The 25-year-old striker joined the Serie A club on a four-year deal on Friday, bringing to an end his six-year association with Villarreal, and the ex-Manchester United man revealed Fiorentina were the only side to truly convince him of their ambition.
Villarreal may now be contending in the second tier of Spanish football but Rossi has fond memories of the east coast outfit's European campaigns, most notably a run to the quarter-finals of the Champions League in the 2008-09 season.
The America-born striker, who has not played since suffering a knee ligament injury in October 2011, said: "I would have made this choice if they'd approached me in the summer.
"I'm very happy to be here at Fiorentina, it's a great club, and the only one who approached me with hard facts rather than just chit-chat.
"I hope to recover as soon as possible so I can start playing in front of the Florence public. The reception they gave me was fantastic and I will remember it forever.
"The team and the club has improved a lot and they play the same kind of football Villarreal were playing five or six years ago - the best there was in Spain."
The former Parma striker is expected to make his long-awaited return to action in March, having undergone surgery on his damaged ligaments three times in less than 18 months.
"This is a new project and I'm happy to play a part in it," he added. "They've given me an opportunity to play top-level football again and we are fighting for big prizes like Champions League qualification.
"The most important thing is to stay grounded, we have a good team and are in fourth place, so we can definitely compete for a European place. It's a long championship but anything can happen."
Viola director of sport Daniele Prade confirmed Rossi has a rescission clause inserted in his contract should things not work out at the Stadio Artemio Franchi.
He said: "He's signed a four-year deal with the option of another four years.
"But he has a 35million euro (£28million) rescission clause for the first two years and that will be reduced to 30million (£24million) for the final two."