Question

which was the biggest dinosaur in category of long neck

Answer 1

Brachiosaurus is the longest necked dinosaur...
actually long neck dinosaurs belong to sauropod category and this one is the longest necked in that category

Answer 2

Earlier it was Brachiosaurus but recently scientists found that in this group of titanosaurs a new dinosaur just 2 feet more than Brachiosaurus.... it's the longest till date and the name is Dreadnoughtus