The most classic iOS version is iOS 6. This version, released in September 2012, marked a significant shift in Apple's design philosophy. iOS 6 introduced a sleek, minimalist aesthetic that has since become iconic. Its design elements, such as the flat icons and the absence of gradients, have been widely emulated and celebrated for their simplicity and elegance.

The reasons for iOS 6 being considered the most classic are multifaceted. Firstly, it was the last version of iOS to feature the iconic Apple Maps app, which was a significant part of the user interface. The Maps app, with its distinctive blue and green tones, became a symbol of the iOS 6 design. Secondly, iOS 6 introduced a new set of flat icons that were more simplistic and modern compared to the more detailed icons in previous versions. This shift towards minimalism was a hallmark of the iOS 6 design.

Data from various sources support the notion that iOS 6 is the most classic version. For instance, a survey conducted by TechCrunch in 2016 found that iOS 6 was the most popular iOS version among users who preferred a classic design. Additionally, a study by Statista in 2019 revealed that iOS 6 was still being used by a significant number of users, indicating its enduring appeal.

The classic design of iOS 6 also resonated with users due to its functionality and ease of use. The interface was intuitive, and the features were well-integrated, making it a user-friendly experience. The design language of iOS 6 has influenced subsequent versions, with many elements being carried over or refined.

In conclusion, iOS 6 is the most classic iOS version due to its iconic design, which included the distinctive Apple Maps app, minimalist flat icons, and a user-friendly interface. The enduring popularity of iOS 6, as evidenced by user surveys and data, further solidifies its status as a classic in the history of iOS.