Honestly this is a very unique and good question.
I would have to go with my mouth! The reason is because my mouth is used for more than one thing! It has several usages, or at the very least more than just one usage.
The mouth allows me to speak to folks and of course eat!
Eyes for seeing, ears for hearing, nose for smelling, and etc.. All great choices but the mouth for me has more than one great usage.
XD