Beyonce has better technique. Her chromatic riffs and runs are unbeatable as well as her lower register.

Kelly however slays Beyonce in belts, and especially upper belts. She pretty much slays anyone with the exception of a few in upper belting.

Their head voice is probably even. With Kelly having more range in it and Bey having more control, although I prefer Kellys tone.

Overall I choose Kelly because I prefer her tone and her power in those belts, and I feel Bey sometimes distracts with her melissimas. I feel that Kelly is the best of both worlds between Bey and Christina.