Shaq -- Best Athlete Dancer Ever ... Says Famous Dancer Dude

What's 7'1, 320 pounds and moves like Usher?

According to "You Got Served" Star Ivan "Flipz" Velez it's Shaquille O'Neal ... 'cause he tells TMZ Sports that no athlete has ever danced as slick as The Diesel.

Ivan -- who's also a world famous break dancer who specializes in head spinning -- was out in L.A. when we asked him which pro baller has the best moves OFF the court, field, or diamond.

Check out the clip -- Ivan says he's been sold on Shaq's dance prowess ever since he busted out some crazy skills during a battle with LeBron at the '07 All Star Game.

LeBron, you got served ...