Mailing Questions

I am wanting to do a mailing to owners of condemed, and red tagged homes and had a couple of questions.
First, is it better to send a letter or a post card?
Second, could someone give me a couple of examples of letters or postcards that they have used and have found effective?
Thank you for the help.
Surri

use the search function on the top middle by your name with the globe try the marketing forum you should find a lot of info already posted on this