To avoid nesting and ngSwitch, there is also this possibility, which leverages the way logical operators work in Javascript:
<ng-container *ngIf="foo === 1; then first; else (foo === 2 && second) || (foo === 3 && third)"></ng-container>
<ng-template #first>First</ng-template>
<ng-template #second>Second</ng-template>
<ng-template #third>Third</ng-template>