1. Scalability and Platform Support: Azure Notification Hubs is a cloud-based service provided by Microsoft, which offers a highly scalable and robust infrastructure for sending push notifications to a large number of devices across multiple platforms, including iOS, Android, Windows, and more. On the other hand, Push.js is a JavaScript library that primarily focuses on sending push notifications to web browsers, making it more suited for web applications.

2. Features and Functionality: Azure Notification Hubs provides various advanced features like tag-based and template-based notifications, scheduled notifications, and audience segmentation based on different criteria. It also supports user registration and management, as well as integration with Azure services. In contrast, Push.js offers a simpler set of features, mainly focused on basic notification triggering and handling, without advanced features like audience segmentation or integration with other services.

3. Push Notification Types: Azure Notification Hubs supports different types of notifications, including badge, toast, tile, and raw push notifications for mobile platforms, allowing for a richer and more interactive user experience. Push.js, on the other hand, primarily focuses on basic text notifications for web browsers, without support for platform-specific notification types.

4. Integration and Backend Services: Azure Notification Hubs integrates well with various backend services and platforms, including Azure Mobile Apps, Azure Functions, and Firebase Cloud Messaging. It provides a comprehensive backend infrastructure for managing and sending push notifications. Push.js, being a JavaScript library, can be easily integrated into any web application without specific backend dependencies, making it more flexible in terms of integration options.

5. Development and Deployment: Azure Notification Hubs requires the setup of an Azure subscription and configuration of specific settings, which might require a certain level of technical expertise and administrative rights. On the other hand, Push.js can be simply included as a JavaScript library in the web application code, without the need for any additional setup or configuration, making it easier and quicker to implement.

6. Pricing: Azure Notification Hubs follows a tier-based pricing model, with costs based on the number of active devices and the number of push notification operations. It may incur additional costs for using certain advanced features or integration with other Azure services. Push.js, being an open-source JavaScript library, is free to use and does not have any associated costs.

In Summary, Azure Notification Hubs provides a scalable and feature-rich solution for sending push notifications across multiple platforms, with extensive backend integration options. Push.js, on the other hand, is a lightweight and simple JavaScript library focused on web browsers, without advanced features or backend dependencies, making it easier to implement and free to use.