Jolly is best for cranidos. Give him rockpolish too, so he can outspeed almost all pokemon and cause havoc. Even with Jolly Rampadros can have attack in the 420's.. add Stabbed Head Smash/Stone Edge(or rockslide for better accuracy), and earthquake, pursuit/zen headbutt, that's one nasty pokemon.
You can use Life orb on it for even more power.. ouch.