what is better to use ajax or angular js
You can't compare as AJAX provides a way to communicate (send requests and get responses) with the server asynchronously and AngularJS used AJAX to extends the 2-way data binding.
To accomplish the above situation we can use Angular $http service.
var baseUrl = API.openweathermap.org/data/2.5/forecast/city;
var method = 'GET';
var data = {};
var params = {
"name":cityName,
"APPID":key_value
};
$http({
method: method,
url: baseUrl,
params : params,
data : data
}).then(function mySucces(response) {
$scope.data = response.data;
}, function myError(response) {
$scope.data = response.statusText;
});