I am developing a web application (ASP.NET, ReactJS) to get various metrics from Jira Server.
Tell me, in what cases is it better to use the Atlassian SDK, and in which REST APIs?
I would say you go with the SDK, since based on experience, performance wise it is much faster and can be easily adjusted to what your needs are.
What SDK are you talking about?
There is an official SDK from Atlassian, and there is an Atlassian .NET SDK (not official)