I think the guitar would be a great choice for you. Guitar chord charts are very straightforward and have nothing to do with reading sheet music. A piano teacher (unless they are a very esoteric kind of piano teacher) is going to get you to start reading music too, and you might find a traditional piano lesson course very slow and frustrating.

Once you learn about four chords on the guitar, you can sing along and really have a great deal of fun very soon. But a half dozen lessons would be great and group lessons are also a great idea.

Happy exploring.