Of the two calls – $.ajax() is the most configurable. You get fine grained control over HTTP headers and you also get direct access to the XHR-object. Slightly better error-handling is also provided but you have to deal with the returned data yourself using a callback.
$.get() is a shorthand for $.ajax() – when using jQuery.get() you pass in an object, and not arguments. The minimum required arguments are the URL of the file you want to retrieve (i.e. ‘test.txt’) and a success callback.