If you ever go to Madrid, don't ever miss a delicious Bocata de Calamares. But, what if you go to the USA? Have a look at the Lonely Planet website and read the article A field guide to 20 great regional sandwiches of the USA and post a comment.
Choose one and say why you think it's the best one, maybe you like the ingredients, or maybe you are interested in the region where the sandwhich can be found. Then say which one you would never give a chance.