Sara - on the Sea Princess, Lago's (the pizzareia) is located inside on Deck 8 on the top level of the atrium. It is sitdown service and you order off a menu. They also offer a trattoria service in the evening.
On the Grand, the pizzareia (sp?) is located outside near the pool (I think it is Neptune's pool) and most of the time pizza is ordered by the slice (but I guess you can request a whole pie.)
On the whole, I much prefered the pizza on the Sea to that on the Grand. jmho
Grand pizza wasn't as good in November as it had been when I sailed on the Grand the first time. I think if you get it right out of the oven it's better. I do prefer the setup on the Grand because it's nice to drop by just for a slice. With all the good food on board I don't want to make a meal out of pizza. And the hot dogs at the grill are terrific too.