I wrote a much longer and more detailed answer but this website timed out and lost it. I should have copied the text before I hit submit. Here's the short version.
Both make sense. Neither are incorrect. But they are different in their meaning.
Note: The evolution of the English language in its various forms allows for both, especially when we take into account a) the lack of historical standardization of language prior to the proliferation of dictionaries and also b) the sometimes arbitrary choices that have been made by early dictionary writers. These factors have caused a lot of confusion in etymology and at the same time, the evolution of language through new uses of words passing into the colloquial and then becoming accepted as literary through sheer frequency of use, is also worth acknowledging.
I believe that the phrase "say your peace" pertains to saying "that which will give you satisfaction or peace of mind."
In the related reference to "hold your peace" from the traditional wedding vow, "peace" in this instance most likely refers to "pact"
nfire:
What absolute nonsense! There is no question. It means 'be quiet'. In, for example Twelfth Night (written at about the same time as the source of the marriage ceremony) there is this song:
Hold thy peace
I prithee hold thy peace
Thou knave.
It obviously means 'be quiet'
meaning the wedding contract, which historically involved dowry and various conditions that had to be met before the marriage could actually occur.
That's true, but irrelevant.
Therefore to "forever hold your peace" would mean to publicly "agree to your contract" without further objection and thus tacitly acknowledge the fulfillment of that contract.
No. The people to whom this is addressed are not parties to the contract. They are observers/supporters. They are being told 'If you know of any reason for the wedding not to go ahead, say it now. Don't go around after the wedding saying the contract was invalid from the start.'
Alternatively, the usage of "piece" likely derives either from Germanic applications of the word "stück" and its possible use at various points in the history of the English language
What possible relevance has this to the discussion?
or it may have been introduced through colloquial use possibly through the common adoption of journalistic terminology as in "opinion piece" "think piece" or "piece of writing". The phrases "piece of music" and "piece of art" also come to mind.
I personally choose to use "peace" with this particular phrase as I believe it to be more historically accurate
Why? It's just NOT.
and have a greater emotional impact as it also implies a sense of importance and finality.
To "say your peace" means to say that which will satisfy some important issue or at least satisfy the need to let it be known.
To "say your piece" means simply to say "that thing you want to say" and it could be as simplistic as that.
Either work, but they have different sentiments.
Let's see which one makes it into the 30th Century Edition of the English Dictionary.