I know that the Angular-UI team has worked hard to remove all jQuery and Bootstrap dependencies from their code, the same as Angular Strap. They both support Bootstrap 3x so you gain nothing by going with a specific library from that perspective either. It really comes down to what features are implemented between the two.
If there are features you need that Angular Strap has that Angular-UI doesn't go with Angular Strap. The same can be said for Angular-UI. It really gets down to which one best fits your development.
