Pica's fruit can only controls certain amount of stone, otherwise he could just take full control of Dressrosa since it's an island full of stone and bedrocks. So Pica's fruit caps out at mountain size.
Pizarro's fruit can take control of an island itself, and it doesn't seem to be limited by any kinds of natural materials. Meaning that Pizarro could take control of sand island, volcanic island, etc. if he has access to them.
HOWEVER, the drawback of Pizarro taking damage when parts of his island got hit is a fucking ridiculous weakness that it pains me to say it, but Pica's fruit is seemingly better utility wise.
Hoping that Pizarro can at least coat his island in strong armament haki or awaken his fruit so his island wouldn't take any damage. But until then, Pica's fruit > Pizarro's fruit.