In general, you should choose a detector with labels similar to the things you’d like to search your collection for. If you’re going to search your collection for specific faces, you should index it with a face detector. If you’re going to search for specific cars, index with a detector that can distinguish between different makes and models of cars.
If you want to find all the instances of a particular object in your collection, you should index with a detector that has a label for that object. For example, if you were looking for airplanes, you could index your collection with a detector that has an airplane label. Then you could search your collection for all media that had an airplane score above a particular threshold.