I have yet to see a first x Beddy whippet with enough class to be called a superb rabbit dog. They often seem to lack in pace, size and often have the terrier trait of being hard mouthed.
I am sure there are exceptions.
Forget a certain cross, just look for dogs who are bred to do the job and most importantly HAVE been doing the job for several seasons to a decent standard. ie. Marking, covering nets, catching, jumping, retrieving (preferably with a soft mouth) biddable etc.