I never really tried Squall, so I am not able to compare him to Tidus.
Tidus is very good if you like to counterattack because of his "Dodge & ..." attacks, which if mastered, have a HP-Attack Combo. If you master Tidus's moves some enemy attacks become useless - unless you make a mistake.
With "Dodge & Slash" you can counter Clouds "Braver" without giving him the time of evading.
With the right use of "Gemetzel" - sorry I do not remember the english expression - Artemisias "Apocalypse" becomes useless
Most of Chaos BRV-Attacks are useless because of "Dodge & Slash"
Hmm... I am promoting Tidus... :P
Well I should become some PR-Guy-Thingy^^