UC, I may have got the wrong impression from your post, but the gunblade isn't a ranged weapon. It's trigger is used to charge the blade, leading to a more powerful attack if your timing is right.

As for the fight, realistically, Squall or Zidane would win. Squall's weapon is far superior to the Buster Sword, Zidane's weapons and Tidus's weapons, and as mentioned before Zidane > Kuja > Mega Flare. It all comes down to whether Zidane could outlast Squall. As for Tidus vs Cloud, I imagine it being rather similar to the Hoppie-Jackhammer Smit bout, for anyone who's read The Power of One. Tidus hands down.