or more importantly, which one that most people tend to stay with it long enough to make something out of it.
Piano is boring because you are alone. Guitar is the same, you make no friend. Now the violin will allow you to join the symphony in school but if you look at a symphony of any school you will see that they are very quiet and strict, no fun, for nerds and geeks only. So I recommend a flute or a clarinet so you can join a band, alot more fun.