Lets broaden the question a bit. If you like the big hairy dogs, do you breed cross to cross, or do you put a pure Deerhound back in now and again ? Simarly, if you like Collie crosses, do you breed cross to cross, or do you add a pure Collie from time to time ? I don't have a preference, I have Lurcher to Lurcher and 1st cross. Some,like Dan ,breed best worker to best worker and others like to put a Pure back in now and again. I used Greyhound and Saluki as an example, as these seem to be the most popular "base" breeds.
Cheers.