If we're really going to be correct, panani means "little breads." The singular is panino. There is no such thing as paninis....you don't need to pluralize what is already plural.
Best Panini New York 2009 - Ballaró
We've come to think of panini as toasted, pressed deli sandwiches, like those you can get at Pax, the scourge of the earth. But "panini" just means "bread" or "rolls"—simply, it's a sandwich of any sort. At Ballaró, temple to the cured pig leg and all the wonderful things that issue from it, find marvelous cold-cut-stuffed paninis on focaccia or semolina bread. Best of all these sandwiches is the one that combines mortadella, primosale (a young, Sicilian sheeps'-milk cheese), and marinated artichokes. The rich mortadella (request the one with embedded pistachios) spins out of control when matched with the tart artichokes and salty Southern cheese.