Fat, protein, and fiber percentages are the biggest differences between those bags, along with their ingredients varying some. Calcium to phosphorus ratios are different as well. Mostly depends on what you're breeding for, how often your does are bred, what else you are feeding your rabbits, etc. Purina Professional might be better if you are breeding for meat and breed often, but complete might be better if you are raising pet rabbits and only breed occasionally. The show bag has a higher fat percentage, so it would probably not be the best for pet rabbits. Those are some of the things that go into deciding on a pellet, in addition to prices.
My rabbits love the taste of Purina Professional (gray bag) and refuse to eat any other brand. I get amazing results feeding it, but things like that vary for every breeder and their rabbits. I have also used the complete for my bucks at times. They didn't like it as much as the professional, but they did at least eat it better than any other brand. I prefer to keep my rabbits all on the same feed, so I stopped feeding the complete to the bucks.
