When managing multiple third-party APIs for a web application, prioritizing them effectively is essential for maintaining seamless functionality. Start by evaluating API reliability, as selecting those with high uptime and strong support ensures consistent performance. Assess the relevance of each API’s functionality to your application's core features, focusing on those that are critical for user experience. Additionally, analyze the integration complexity; opting for APIs that are easier to implement and maintain can save development time and minimize potential issues down the line. Establishing these criteria will help streamline your decision-making process and enhance your web application’s overall performance.

When working with multiple third-party APIs in a web application, I’d prioritize based on three main factors: functionality, reliability, and integration ease. First, I'd assess which APIs are essential to the core functionality of the app—these are non-negotiable and go straight to the top of the list. Next, I'd look into the reliability and performance of each API, considering both speed and uptime, because any downtime or lag will impact the user experience. Finally, I’d focus on how well the APIs integrate with the existing tech stack, preferring those that are straightforward to implement and maintain. This approach ensures I'm using the most critical, dependable, and compatible APIs first.

According to my point of view the priority should be given to the one which is easy to integrate, because sometimes integration of third party APIs are too complex and require a lot of back and forth debugging to integrate within application. By integrating the easier ones not only we will save time but also focus on the complex at a later stage thus not wasting important development time and also completing some stage of application. Also the learning from the one which we completed can be used for the complex integration.

IMHO, when dealing with long process APIs, I implement callback patterns to prevent system delays. For non-urgent operations where immediate responses aren't needed, I prefer async methods. If an API times out, I will use simple retry mechanisms in the user interface. From my experience, it's more important to have steady, reliable service than quick but unpredictable responses - I'd rather have an API that takes 1.5 seconds but works 99.9% of the time than one that responds in 0.5 seconds but fails frequently. The key is maintaining system stability while ensuring a good user experience through clear error messages and easy retry options when needed.

While working with multiple 3rd party API' in a project it's crucial to maintain the prioritised api and to start with is the alligning them with functional priorities. Then check for the reliability and resilience of the services.. few could be used as a background service with a robust retry mechanism..