Submitting REO Offer: Sales Contract? Offer Form? or Formal Letter?

[David Kimball]

Hi I know that there has been some discussion about the finer points of submitting REO offers. But which is actually the proper format to use - sales contract, offer form, or formal letter?
And if offer form is the way to go, where do I get a good one, or can I just replicate the one an REO agent once emailed me?

Thanks!