OK. If you don’t want to use the correct way ng-options, you can add ng-selected attribute with a condition check logic for the option directive to to make the pre-select work.
<select ng-model="filterCondition.operator">
<option ng-selected="{{operator.value == filterCondition.operator}}"
ng-repeat="operator in operators"
value="{{operator.value}}">
{{operator.displayName}}
</option>
</select>
Working Demo