Which method is best for ensuring environment consistency in deployment?

Utilizing containers is the best method for ensuring environment consistency in deployment because containers encapsulate an application and its dependencies together into a single package. This means that the application can run consistently across different computing environments, whether it's a developer's laptop, a testing environment, or a production server.

Containers provide a standardized way to bundle applications, which eliminates the "it works on my machine" issue typically encountered in software development. They include everything the software needs to run, including libraries, configurations, and other binaries, ensuring that the environment in which the application runs is consistent regardless of where it is deployed.

In contrast, virtual machines provide isolation but can be heavier and more complex to manage, making them less efficient for providing environment consistency especially when scaling. Continuous Integration services facilitate the integration of code changes but do not inherently address the environmental consistency of the applications being deployed. Manual configuration, while possible, is prone to human error and can lead to inconsistencies and discrepancies between environments over time. Hence, utilizing containers is the most effective technique for achieving reliable and reproducible deployment environments.