The four most popular Ruby HTTP libraries, net/http, HTTParty, rest-client, and Faraday, are compared in terms of their convenience, stability, and control over the request/response cycle. Net/http is built into the Ruby standard library but requires more work to use. HTTParty adds convenience methods and works well with RESTful APIs, while rest-client also offers a simple interface but still requires the JSON library for parsing. Faraday provides customization options and control over the middleware, allowing developers to choose from seven HTTP clients. Each library has its strengths and weaknesses, and the choice of which one to use depends on the specific needs of the project.