I'll do my best to piece together a good description of fighting tactics based on scans, interviews, and demos shown.
Jecht: Jecht is an all round fighter. He's not a tank like Garland, nor is he agile like Tidus, or takes to the air like Zidane. So far he seems to be the closest villain to match Light Warriar, combining his ability to take blows with an agile yet brute strength. Clips from demos show him being able to produce very large projectiles in Ex-mode form.
Tidus: Acrobatic and speedy, Tidus can make gaps that most other characters can't. His attack power doesn't seem as strong, and he has limited projectile ability. His exmode increases his speed 2xs his norm, and his attacks hit home more frequently.
Kuja does not use a weapon, but instead uses a ring of orbs. These have the ability to hit anyone around him within a certain distance. He is essentialy able to hit the enemy even if his back is turned, which makes up for what may be a lower defence. His abilities in Trance Mode are yet to be displayed, beyond what apears to be firing Ultima.
Zidane: Zidane has the most aerial ability of the lot, though not as much speed as Tidus. Judging on the fact tha the works with daggers, his combo rate may be another strength. His Dyne abilities have been displayed, showing Shift Break, Solution 9, and Stellar circle although his exmode Finisher has not been shown.
Ultimecia is a spell slinginger. Her attacks are comprised of magical purple projectiles that home in on the enemy. She also has the ability to freeze time and teleport, making a battle with her one of attempting to get near her. She probably has low defence, and these tactics are to evade the blows that would cripple her. When junctioned with Griever in Exmode, she can perform a Renzokuken style barrage of her magic attacks. Her enhancements otherwise in Exmode are undefined. She also apears able to interupt exmode attacks
Squall: Squall is capable of landing the most consequitive hits at any one time. So far only the limit break Rough Divide has been shown powering up, but not used. His exmode finisher is a return of Renzokuken. There's no clear indication of what his Exmode entails, though speculation based on some screenshots show that he transforms into his SeeD uniform.
Onion Knight: Onion Knight is by far the weakest character, but makes up for it with an Exmode that happens much more frequently compaired to the other two battles we've seen. Where he lacks the ability to do real damage in normal form, his exmodes seem to be the most versitile. As a Ninja, his speed rivals that of Tidus and Zidane, and he gains the advantage of two swords. His ex-finisher, he is allowed to pick from a variety of projectiles. As a sage, he can use any number of white or black magic, which may imply he may be the only character capable of healing himself without the fortune of finding a potion. This is notable, as health does not regenerate from battle to battle on its own. He is shown being able to use Firaga, Holy, and Meteor to great effect.
Cloud of Darkness: Cloud of Darkness has a lot of resiliance in the fight she is shown in. Her main way of attacking is by energy attacks, or the use of the two demonoid serpents that escort her every where she goes. But unlike other distanced fighters, these serpents have an element of randomness. Probably to reflect her chaotic, destructive nature, the serpents will swirve all over the playfield, around obsticals, and often completly missing the oponent, unless they fail to be warey of them. She has not been shown performing in Exmode beyond screenshots of her NES styled self.
Firion: Firion is an all round fighter, capable of switching between melee and long distance fighting at will. How this works, and if it involves exmode remains to be seen, as well as the fact that his exmode-finisher has not been displayed. So far he is shown wielding the Axe, Bow, Staff, and Blood Sword.
Emperor: The Emperor has sheer size on his side. He is easily one of the tallest characters after Exdeath. He seems very good at producing comboes with his lance, though his real unique strength seems to be the ability to lay traps that detonate around his opponents.
Light Warriar: Light Warrior is an all rounder, who makes good use of both sword, projectile energy attacks, and his sheild. He is fairly quick and strong, but just as he has no real weakness, he doesn't seem to have any major strengths to speak of. His exmode is to transform into the Knight, though he has not been seen performing in this mode.
Garland: Garland is this game's resident tank. He lacks speed compaired to everyone else, but his weapon has both reach and brutal force behind it. When in Exmode Soul of Chaos, his speed increases, as well as his strength, making him one of the most powerful characters in the game when it comes to measuring sheer strength
