Serena Williams -- Fangirling with Tom Brady ... 'You're My Favorite!' (VIDEO)

Even Serena Williams couldn't contain herself during a face-to-beautiful-face with Tom Brady today ... telling the QB he's her favorite EVER ... and she was so pumped, she needed a moment to recover.

The two met up during a quick photo shoot in NYC Wednesday -- no word on what it was for ... but clearly, Serena was smitten by the QB ... especially after Tom reciprocated the love.