bill - 12:35 am on Dec 11, 2009 (gmt 0) It's not an either/or proposition to me. Do both.
If you have changing content on your site that users would be interested in knowing about then an RSS feed would be a given. You could certainly put newsletter information into an RSS feed, that's what they're used for in many cases.
It's not an either/or proposition to me. Do both.