Which cloud service mentioned allows users to build web applications without concern for server locations?

The correct choice is Google Apps. This cloud service allows users to build and deploy web applications using cloud-based tools and services without needing to worry about the underlying server infrastructure or physical server locations. Google Apps, which encompasses services like Google App Engine, provides a platform for application development that auto-scales and manages resources in the cloud, allowing developers to focus on coding rather than server management.

In contrast, Amazon's EC2 is focused on providing virtual servers where users must configure and manage their own environments, including deciding where to deploy those servers physically. Microsoft Office 365 primarily offers productivity applications and does not focus on application development in the sense of building and deploying applications like Google Apps. Dropbox is fundamentally a file storage and sharing service, not a platform for building web applications. Thus, Google Apps stands out in enabling application development seamlessly in the cloud.