Blue Buffalo or By Nature Cat Food?

I want to change my cat, Stewart's food from Royal Canin to either Blue Buffalo or By Nature. I want to know which one is better. He's on By Nature wet food and loves it. So I'm leaning toward By Nature, I just want a second opinion. The kinds of By Nature I was looking at was the adult cat formula and the 7 seafood platter. The Blue Buffalo I was looking at was the adult indoor formula, the select chicken and brown rice adult cat formula, and salmon and rice adult formula. thanks in advance.