The main difference between Apple AirPods 3 and AirPods Pro lies in their design, fit, and additional features. AirPods Pro offer a customizable fit with interchangeable silicone ear tips and advanced noise cancellation capabilities. They also feature a Transparency mode, allowing users to hear external sounds when needed. On the other hand, AirPods 3 have a standard design with a comfortable in-ear fit, providing a balance between convenience and sound quality.