ok, realistically, squall would win. theres no question. you see, a "gun" fires a "bullet" which "kills" said "victim". and theres no dodging it, cuz it goes at the speed of sound. however, if you want to go realistically to the point where gunblades dont exist, zidane would win, as no one can actually wield a buster sword properly, especially since cloud has incredibly small muscles. and zidane is just more skilled then tidus hands down.