Costa Magica Dining - Smeralda vs Portofino

Hi,

We have the option to choose between early and main dinner, i.e 7pm or 9m. With late dinner we can only choose Portofino.

Is one restaurant better than the other? Is the food served different? Is there a fixed schedule, e.g. can we show up at 9:30 for main dinner, or 8:15 for early dinner, or does everyone have to be seated at the same time?

Thanks. ;)