"Sí, gracias, yo quiero un sándwich."
Translation:Yes, thank you, I want a sandwich.
Well, sándwich is sort of a non-Spanish word that was picked up out of English. Emparedado is the original Spanish word. So its usage is based on the region. (You would definitely use emparedado in Spain, and possibly the other in Mexico)
Emparedado is actually a word created for people to stop using sándwich, which never happened. The last time I saw a Spaniard hear the word emparedado he just laughed.