You should say your piece and hold your peace.
Have you ever wondered about the difference in the two sayings, "hold your peace" and "say your piece"? They seem to reference the same thing: whether or not to keep your mouth shut, but these are two very different idioms.
If you say your piece, you are saying your part. You have a piece of information to contribute, and you are saying it. Hence, "say your piece".
The second, familiar thanks to conservative and often outdated Christian wedding ceremonies, is "speak now or forever hold your peace". In other words, if you know of anything that would cause a disruption in this lifetime partnership, you'd better either spill it or take it to your grave. Basically, make your peace with zipping your lips.
Makes me wonder: What if I held my peace, but now need to say my piece? Grammatically, it's correct, but I think friends may be lost if this happens. Eeek!