Docker is a containerization technology that allows developers to ship software applications along with their dependencies in Docker images. Developers can extend existing images using them as base images when writing Dockerfiles. However, a lot of alternative functionally-equivalent base images are available. While many studies define and evaluate quality features that can be extracted from Docker artifacts, it is still unclear what are the criteria on which developers choose a base image over another. In this paper, we aim to fill this gap. First, we conduct a literature review through which we define a taxonomy of quality features, identifying two main groups: Configuration-related features (i.e., mainly related to the Dockerfile and image build process), and externally observable features (i.e., what the Docker image users can observe). Second, we ran an empirical study considering the developers’ preference for 2,441 Docker images in 1,911 open-source software projects. We want to understand (i) how the externally observable features influence the developers’ preferences, and (ii) how they are related to the configuration-related features. Our results pave the way to the definition of a reliable quality measure for Docker artifacts, along with tools that support developers for a quality-aware development of them