AngularJS ngRepeat and orderBy.

HTML

<div ng-app="myApp" ng-controller="Ctrl">
  <div ng-repeat="card in myCards | orderBy:sortByEitherDate">
    <businesscard>{{card.lastName}}</businesscard>
  </div>
</div>

JavaScript

angular.module('myApp', [])
  .controller('Ctrl', function($scope) {
    $scope.myCards = [{
      actualStartDate: 'John',
      lastName: '3'
    }, {
      estimatedStartDate: 'Eleanor',
      lastName: '2'
    }, {
      estimatedStartDate: 'Maxwell',
      lastName: '4'
    }, {
      actualStartDate: 'Buzz',
      lastName: '1'
    }, {
      actualStartDate: 'Neil',
      lastName: '5'
    }];

    $scope.sortByEitherDate = function(row) {
      if (row.actualStartDate) {
        return row.actualStartDate;
      }
      return row.estimatedStartDate;
    }
  });