Multiple identical mailings or different every time?

[Al Bunch]

Working up some direct mail pieces and wanted to get some input from anyone who does direct mail on a regular basis. Would you recommend sending the same mailing piece every time or would you mix it up sending a new piece each time or repeat the first piece 2-3 times then the next piece 2-3 times?

I can obviously run trials to see what works better, but if you've done it before, I'd definitely like to hear your thoughts.