There is no one-size-fits-all answer to this question, as the best direct mail campaign will vary depending on a company's specific goals and target audience. However, some key elements of successful B2B direct mail campaigns include personalization, a clear call to action, and an attention-grabbing design. Additionally, it can be helpful to incorporate multi-channel marketing tactics and track metrics to measure the effectiveness of the campaign. Ultimately, the best campaign is one that achieves its intended objectives and generates a positive return on investment.