Burger King has much higher variability than McDonald's. Corporate is far looser with standards and more hands off with franchisees. The equipment used is far less standardized, staffing levels and procedures is mostly up to the location owner. I suspect that Burger King franchisees own more locations than is the case with McDonald's. Burger King can be alright if it has a good owner but terrible if there's a bad owner, like the locations in Atlanta owned by Magic Johnson.
As for Chick-fil-a, franchisees are limited to one location and they must work it full time. That puts them in a completely different world than McD's or BK.