Candidly, I have found that no one method works exceptionally well. Each has yielded great and poor results at different times. As far as response rate, email has about 5% to 10% but the email addresses are vetted and verified. Cold calling is about the same, although prepare to be hung up on or have unpleasant words said to you from time to time. Postal letters typically give 3% to 7% but I have had 100% response on one campaign that I sent out. In short, try each one and track your results, which will vary widely based on industry and geographical location.

Thanks David for sharing your experience.