In terms of the menu, BK has mutton which is not on KFC/McD menus. BK has created a menu at the intersection of McD and KFC - Burgers, Wraps, Nuggets, and Chicken Wings including Boneless and Grilled Chicken. (Plus a little nudge into Taco Bell territory with Veg/Chicken Tacos)
The domination of non-veg items in the menu is bound to give BK a higher per-order value and they should in fact make sure they are priced higher than McD on most items to have the premium factor, other than some value offerings which they can retain to compete for the lower-order value customers.
On the question of people preferring one brand over the other, I feel like each brand will develop its loyal customers and over time price will not be such a big factor, just as McDonald’s offerings have gone far beyond the low-price value items and into McCafe + Gourmet burgers category.
While a smaller point, I also feel McDonald’s success so far could become a positive for other brands as just being located in the same food courts/malls could see other brands gain from McD’s waiting time