If you are using Angularjs, then you should use $http as the preferred method of making the ajax calls.
It is not necessary for that service to be binded to ui or be affecting ui.
You should use Jquery Ajax calls only when you are unable to perform the action using angular services which will be rare if you follow angularjs best practices.
Also if you use http services, you can have intercepters that creates requests and processes response before they are given to success part of the call. These are used for handling global errors and displaying global notifications which let's say, can come in any response. Plus you can add headers and more info before each request here. Also you can encode/decode the request/response here such that all these utility functions are done at the same place. Check the below link for this:
http service doc with interceptors
If still you need to call the $http from outside angular environment, which you should try to avoid, make a common utility function of angular and wrap it in some function that you can call directly.