Different sites can have different rankings, but if you don't choose one of them to be the source, then it's just your opinion of which dinosaurs are most popular.
If you can't decide which source to use, or don't want to use just one source, you could do a scholarly aggregation of the different sources and publish your original research as the source for this quiz. Too much work? I don't blame you. So pick a source and don't worry about the fact that other sources will differ.
'Tyrannosaurus' is the universal term 'Rex' is referring to an exact species of tyrannosaurus while all dinosaurs have their own separate species of the same name
I would argue that there are several dinosaurs more beloved and popular than Iguanadon. For example Apatosaurus, Diplodocus, Ankylosaurus, Utahraptor or even Gallimimus.
If you can't decide which source to use, or don't want to use just one source, you could do a scholarly aggregation of the different sources and publish your original research as the source for this quiz. Too much work? I don't blame you. So pick a source and don't worry about the fact that other sources will differ.