AngularJs: How make ui-select working properly?

I don't know what the situation was like before Select2#4.0, but it's really not all that hard to use it without angular-ui-select (and it's one less dependency)

Just include select2 in your bower dependencies and use it in your link function within the directive:

.directive('someDirective', function() {
    return {
        restrict: 'E',
        link: function(scope, element, attrs) {
            element.find('.your-select2').select2({
                theme: 'classic',
                placeholder: 'Select a placeholder...',
                allowClear: true,
                data: [{ id: 'New', text: 'New'}]...
            });
        },
    };
})

and your HTML:

<select class="your-select2" ng-model="a.model.field"></select>

You can also load the data from the controller via a service if you want, then just use the scope to set it!

I say this as I tried using angular-ui-select because I thought "hey it's Angular, you must use a plugin for it!", but that's not always the case :). Plus I found the docs not so helpful (call me lazy but hey)

You haven't been particularly descriptive with the errors you're seeing so I don't know if the following will help..

I had a problem originally when using the ui-select demo code as an example because they're using the propsFilter filter which is a custom filter they have written for the demo:

<ui-select-choices repeat="tag in all_tags | propsFilter: {name: $select.search}">

I am assuming you're not including this filter in your code which may be a reason you're experiencing a problem. You can resolve it by using angular's normal filter:

<ui-select-choices repeat="tag in all_tags | filter: {name: $select.search}">

Alternatively, if you have multiple properties to filter you can write the propsFilter filter to filter on OR rather than AND. If you use 'filter' to filter multiple properties it will try to match the search value across all of the properties.

app.filter('propsFilter', function() {
  return function(items, props) {
            var out = [];
                if (angular.isArray(items)) {
                  items.forEach(function(item) {
                        var itemMatches = false;

                        var keys = Object.keys(props);
                        for (var i = 0; i < keys.length; i++) {
                              var prop = keys[i];
                              var text = props[prop].toLowerCase();
                              if (item[prop].toString().toLowerCase().indexOf(text) !== -1) {
                                    itemMatches = true;
                                    break;
                                  }
                            }

                            if (itemMatches) {
                              out.push(item);
                            }
                      });
                } else {
                  // Let the output be the input untouched
                      out = items;
                }

                return out;
          };
    });

you can see the commit with the filter in it here: https://github.com/angular-ui/ui-select/commit/3fac88cfad0ad2369c567142eadba52bdb7998b1

Although if you have some specific filtering requirements I would recommend you to write your own filter to ensure optimum performance.