What is the best belay carabiner to use with a Grigri device for optimal safety and performance?

The best belay carabiner to use with a Grigri device for optimal safety and performance is a pear-shaped carabiner with a round stock and a keylock nose. This type of carabiner provides smooth rope handling, reduces the risk of cross-loading, and minimizes the chance of the carabiner getting caught on gear or the rope.