This an interesting statement. I don't know what the context was, or if you are just constructing it yourself, but this is the kind of statement that is most effective when you use a parallel construction. By this I mean, you are comparing two things here: what you say to me ... and ... what I say to myself. And so the impact of your statement will be strongest on the listener when this parallel comparison is stated clearly and concisely. Consider this revision ... Whatever you say to me will never be worse than what I say to myself. Conciseness is achieved by using simpler verb forms -- "is never going to be" becomes "will never be", and "would say" becomes, simply, "say". Note: Erase the word "gonna" from your formal written vocabulary. It is not English :)

Whatever you say to me is never gonna be worse than I would say to myself. Of course, "gonna" is slang for "going to". It's very informal. So the more correct sentence would be: Whatever you say to me is never going to be worse than I would say to myself.