The Knight isn't all that much different than the Warrior, continuing to use all the best Weapons and Armor. The main upgrade here is that they can use level 1–3 white magic. The big highlight Spell here is Blink, though you will often just be using the Knight's Spell slots as extra cures. They are still a solid Class, and the best tank in the game. Once you get Excalibur they can really bring the hurt.
The KNIGHT isn't all that much different than the FIGHTER, continuing to use all the best Weapons and Armor. The main upgrade here is that they can use level 1–3 white magic. The big highlight Spell here is RUSE, though you will often just be using the KNIGHT's Spell slots as extra CUREs. They are still a solid Class, and the best tank in the game. Once you get Xcalber they can really bring the hurt.
The Knight is simply an improved Warrior. They can't use the low-level bows the Warrior can, but other than that they're just Warriors, but better. They also automatically take hits in place of any party member that is low on HP. Switch any Warriors you're using to a Knight immediately and don't look back. While Knights are initially outclassed by several Water Crystal Jobs, once you start finding top-tier swords like the Defender, they once again become a powerful Job option.
As a Paladin, Cecil becomes your best front-line fighter. He can use the best Armor in the game, as well as powerful swords, and even has access to basic White Magic. His Cure1Spell is great for saving other Characters' MP when healing outside of combat, and the fact that he gets Esuna and Exit is just a bonus. His Cover ability is also excellent. He will automatically take physical hits for any party member that's low on HP, but you can manually Cover a party member and take hits for them regardless. This is invaluable for protecting weak mages in important fights.