I would pick Tidus here. Not only does Tidus have Squall beat on the level of athletic ability and agility, but he's also got the motivation and spunkness to keep his head up in the fight even if Squall would deliver a strong blow to Tidus. When I picture Squall taking on someone in a one-on-one battle, I seem to refer back to the opening of FFVIII and the fight vs. Sefier. I can see Tidus landing a few more gashes on Squall's face.