I rather like Mojoceratops – like Triceratops, but with an even sillier name.
But yeah, if we’re sticking to proper dinosaurs from when we were kids, and not silly newfangled ones that paleontologists make up so they can file their PhD theses, I’d have to go for Triceratops. I had a model one when I was small, he was double-hard and could beat all the other toys, even the Transformers.