If you kept the question at a higher level, paladin vs druid, I would probably say a holy paladin as they are near unkillable and can turn the tide of a battle. Resto druids are good too but the pallies plate and mana efficiency shine through.
But back to your original question, feral druid or ret pally, I would have to say feral druid anytime. I know Esfand is the ret pally gold standard but you are going to spend a lot of time and effort trying to get close to what he does. Feral druids offer you a lot of flexibility and I don't think there is any 1 class that is anti-druid.