I do a similar sort of thing - I will never buy my dog food with poultry or pig in it as they use by far the most cruel farming methods (In britain anyway). from what I gather rabbit is usually farmed in small cages or hutches, although the local butchers around me sell rabbit that has been shot by farmers/ teenage boys as pest control and to earn a bit of money. I would say wild venison would be best, followed by lamb which (in britain) is just about always reared outside for their whole lives. after that would probably come farmed venison, then beef.
Organic should be a safe bet too as (again, in britain -not sure about the rest of the world) as they have strict welfare standards.