If you have an accident and it wasn’t your fault, you have no way of controlling which of the five insurers will deal with your claim. The insurer managing your claim will be the insurer of the vehicle that caused your accident.
If you have family or friends that you regularly drive around in your car and you are the perfect driver, driving in a perfect world where every other driver is perfect then you won’t care who your Green Slip insurer is because, as the perfect driver, no one is every going to make a claim against you. But if you are a human being driving in the real world, where you might make a mistake and cause an accident, when your car is occupied by your nearest and dearest, then something other than price might motivate you to choose your Green Slip insurer. I would suggest you want an insurer who is going to get your kids the best recovery possible, an insurer who is going to pay your spouse’s income while they cannot work and do so quickly and pleasantly.